A Obilictro Ics - American Radio History

Transcript

A ObILICTRO ICS CONSTRUCTOR -R 28MHz RECEIVER www.americanradiohistory.com Each £3 unit of Home Unit Insurance gives you protection up to the limit shown This is the simplified insurance you have been waiting for. (or # units after the first) up to a maximum of five. So Not just cover on the contents of your home but a simple. So easy. Apply to your Broker, Agent or local office package of personal protection you and your family need. of a General Accident company. And it's how we save you so much money: just ONE The Home Unit Policy can replace your existing insurances policy to issue instead of nine! And remember- as you buy more possessions just add You can build up to the cover you need by additional units more Home Units at any time. Quote Ref. 20/9468 THE GENERAL ACCIDENT FIRE & LIFE ASSURANCE CORPORATION LTD Metropolitan House, 35 Victoria Avenue, Southend-on-Sea, Essex, SS2 6BT Please send me further particulars of the Home Unit Insurance. Name Address Itpays to beprotectedbya 20/9468 www.americanradiohistory.com 13IPRE-PAK Bargains in Semi -Conductors, components, modules & equipment. Bargains from our FREE Catalogue challenging values! 20 large pages, filled with real bargains in transistors, I.Cs, components, equipment, etc. Send large S.A.E. with 7p stamp for your FREE copy of 6th Edition by return. Meanwhile, for prompt delivery order from this month's ad. NOW. Stirling St uni TRANSISTOR PACKS ALL 50p each TESTED AND GUARANTEED Rec. A IN4007 Sil. 1,000PIV diodes. 1 amp. plastic Reed Switches, 1" 10 long 1" dia. Highspeed P.O. type Mixed Diodes, Germ. Gold bonded, etc. Marked and Unmarked Short lead Transistors, NPN Silicon Planar types B79 B81 H39 H65 H38 30 H66 50 .0 B66 150 B84 100 B86 4 gates circuits BMC 962, flip flops BMC 945 BD131/B0132 H2O Diodes sub. min. H67 H34 glassequiv.to0A200, 0A202 Plastic Transistors A 40361 Type NPN Transistors TO -5 comp. to H66 A 40362. Type PNP `f Transistors TO -5 comp. to H65 Sil. can and IN916 BY126/7 Type Silicon 15 Rectifiers 1 amp. plastic. Mixed volts Power Transistors, PNP. Germ. NPN Silicon TO -3 Can 3819N Channel FET's plastic case type L 10 SILICON POWER TRANSISTORS VCE 40N2 Gain 15 40 40P1 15 15 40P2 90 WATT 40 40 90N1 15 15 40 40 90P1 15 15 90P2 40 40 NPN NPN PNP PNP 20p 30p 20p 30p NPN NPN PNP PNP 25p 35p 25p 35p Essential for Colour T.V. alignment of 4 patterns. Featuring plug in IC's and a more sensitive sync. pick-up circuit. The case is virtually unbreak- & able -ideal for the engineer's toolbox -only measures 3" x 51" x 3". Operates from 3 U.2 type batteries ' (extra). Completa rte/ Ready built kit unit only Op £7.93 CAPACITOR DISCHARGE IGNITION UNITS £7.50 Compact I.C. amp. with 3 watts R.M.S. output. Operating voltage 6 to 22. Size 31" x2" SS.103-3 Stereo version of above using one I.C. on each channel SS.105 A compact and useful all-purpose amplifier which will run excellently on a 12V supply. With 5 watt output, two make a good stereo amp. Size 2}" x l3" SS.110 Similar in size to SS.105 but with a 10 watt output. Ideal for many domestic and small -size PA. applications. Operates from 26 to 32V. SS.140 Excellently designed 40 wan R.M.S. (into 4 ohms) hi-fi amplifier. S/N ratio better than 75dB. THD better than 0.2%. Power requirements-45V. d.c. With 0.15" centre edge connections. Two can be bridged to give 80 watts R. M.S. into4ohms SS.201 SS.202 SS.203 Metrication Pocket Charts 12p. 8 assorted relays £1.00 (8%). Rev. counter device (for cars) £1 00. U.H.F/TV Tuner Units, 625 lines, Rotary Tuning £2.50. L M.380 Audio I.C. £1.00 and technical books of all kinds. orders. POSTAGE Except where stated, add 20p for postage & packing in U.K. Overseas-add £1, any difference being charged or refunded. PAYMENT Cash with order, Cheque or money order. Minimum value -£1. You can also pay by ACCESS. IMPORTANT-Every effort is made to ensure accuracy of prices and description at time of preparing this advertisement and going to press. Prices are subject to alteration without notice. £2.40 £3.60 Ganged tuning condenser with accurately engineer- sensitivity. Tunes 88-108MHz. With A.F.C. facility. Operates from 6V -16V £6.25 I.F. stage (with I.C.) Pre -tuned. A.F.C. connection. Operates from 4.5 to 14V. £5.25 Stereo Decoder. Designed essentially for use with SS.201 and 2, this module can also be used in most mono FM tuners. A LED may be attached. Operating voltage 9-16V. d.c. £5.62 Add this to an unstabilised supply (say typically 45V. output) to obtain a steady powerful working output adjustable from 12 to 60V. Essential for your audio and special systems. Money saving and very reliable. Ideal for workbench use. £3.25 MAINS TRANSFORMERS FOR ABOVE Add 35p P. & P. per transformer Type A 18v/1A (Suit SS. 103) Type B 25v/2A (Suit SS. 110) Type C 30v/2A (Suit SS. 140) Bridge Rectifier Type A 27p Type B/C 38p SS.202 £1.50 £2.00 £3.25 STIRLING SOUND DISCO MINOR TERMS OF BUSINESS V.A.T. Prices shown do NOT include V.A.T. Please add V.A.T. 25% to total value of your order including postage, except for items marked with a e, or (8%) for which the V.A.T. rate is 8%. No V.A.T. on overseas £1.95 POWER SUPPLY STABILIZER MNFRS. AM/FM CHASSIS SUNDRY £3.25 ed slow-motion drive in rugged housing. Excellent SS.300 To clear. NO instructions or tuning drives, useful for experimenters. Not too difficult to get working. Make good portables EACH £1 SS.105 £1.75 THE MODULES TO BUILD A STEREO F.M. TUNER / frp9.93 OVER 1,000,000 TRANSISTORS IN STOCK Transistorised. Simple to Fit. Improves performance, cuts fuel costs P & P add 25p POWER AMPLIFIERS SS.103 - NEW X -HATCH GENERATOR Mk.2 kit or complete Pre -amplifiers: tone control SS.100 Active tone control unit to provide bass, treble, balance and volume controls £1.60 SS.101 Pre -amp for ceramic cartridge, tape and radio £1.60 SS.102 Pre -amp for low output magnetic cartridge, tape and radio. With R.I.AA. correction ...1dB at 1K £2.25 PLASTIC Price 15 40 90N2 P AMPLIFIER MODULES Sil. can 90 types 40 WATT Type 40N1 STIRLING SOUND AUDIO MODULES come to you as basic units assembled on P.C.Bs enabling you to add required components in layouts of your own choice. Modules are tested and boxed before despatched and include well printed instructions. Complementary UNTESTED Et Germanium Transistors PNP,AF and RF Germanium Diodes Min. glass type Silicon Diodes DO -7 100 9 H41 100 B1 u 2 H35 UNMARKED C Integrated 1 Fully transportable. Console fitted twin turntables with cross fade, monitoring, L -R cueing, mic. with over ride. Ampower 40 loudspeaker has built-in mains powered 40 watt RMS power amp. Up to 10 Ampower may be added. With one Ampower and console £100 plus V.A.T. at current rate. Carr. U.K. £3.50 SS.203 SS.300 reMilifflfflMIIIMIMMIMMIIIIII.1-MI To BI-PRE-PAK, 224-226 WEST RD., WESTCLIFF-ON-SEA, ESSEX 1 Please send for which I enclose inc. V.A.T. Name 222 224 WEST ROAD,WESTCLIFF-ON-SEA, ESSEX SSO9DF. TELEPHONE: SOUTHEND10702146344. WRITE ORDER SEPARATELY AND ATTACH COUPON IF REQUIRE JUNE 1975 Address REC 6 ------------J 641 www.americanradiohistory.com HOBBYIST- PROFESSIONAL - DOMESTIC - SURPLUS - INDUSTRIAL JUST AFEW OF OUR BARGAINS ARE LISTED BELOW- SEND STAMPED ADDRESSED ENVELOPE FOR A QUOTE ON OTHER REQUIREMENTS. PAY US A VISIT. OVER 90', OF STOCK BELOW QUANTITY COMPONENTS WHOLESALE PRICE. RETURN POSTAL SERVICE UNLESS CHEQUE. Goods sent at customer's risk, unless sufficient payment for insurance included (2p per VALVE BASES Printed circuit B9A - B7G .. - - Chassis B7 B9G B7G Shrouded chassis B7G B9A B8A - B9A chassis - B12A tube Speaker, 6" - 6p x 4", 5 ohm, ideal for car radio etc. £1 TAG STRIP -6 way 3p 9 way 5p Single 1p 14 glass .. .. 4p 4p 6p fuses- 250 3" tape spools .. WRIST COMPASS 30p with Needle Lock m/a or 3 T03 Mica Washer 2p 18 volt 4 amp charger bridge rectifier 50p GC10/4B Cold Cathode £3.00 Telescopic aerial Closed 91", open 381" Fitted right angle TV plug, 50p amp (box of 12) 18p 8p 25p 5p 60p 30p 40p 50p 10p 30p 30p Brand new Boxed 6K7G PVC or metal clip on M.E.S. bulb holder Geared Knob, Inner to Outer Ratio 8:1 Bulgin, 5mm Jack plug and switched socket (pair) 12 volt solenoid and plunger .. 250 RPM 50 c/s locked frequency miniature mains motor 200 OHM coil, 2k" long, hollow centre Belling Lee white plastic surface coax outlet Box R.S. 12 way standard plug and shell .. .. . SWITCHES Pole Way 4 2 6 2 2 2 2 1 3 4 1 3 2 Type Sub. Min. Slide Slide Lever Slide Slide + off Sub. min. edge 13 amp small rotary 18p 20p 15p 10p 10p 12p RESISTORS watt .. watt Up to 5 watt wire 10 watt wire wound .. 15 watt é-4-2 1 . , . , 1 p 2p 10p 12p 14p £1 Min 5p) U.K. only. ELECTROLYTICS MFD/VOLT. Many others in stock 70200- 300- 450 - Up to 10V 25V 50V 75V 100V 250V 350V 500V MFD 10 4p 5p 25 4p 5p 50 4p 5p 100 5p 6p 250 9p 10p 500 10p 11p 1000 13p 17p 6p 8p 6p 8p 6p 9p 10p 12p 8p 8p 13p 19p 12p 15p 18p 20p 16p 20p 18p 20p 25p -- -- - --- 11p 17p 28p 85p £1 17p 24p 45p 40p 75p £1.50 2000 23p 37p 45p As total number of values are too numerous to list, use this price guide to work out cost of your actual value requirements, i.e. 2MFD, 30V would be 5p, or 330MFD, 50V would be 14p, etc. etc. 8/20, 10/20, 12/20 Tubular tantalum 15p each 16-32/275, 32-32/275, 100-100/150. 100 100/275 50-50/300 .. .. 20p each 12,000/12, 32L32-50/300, 700/200, 100-100100-150-150/320 .. 50p each 20-20-20/350 .. .. 40p each INDICATORS vol D676 red, takes M.E.S. bulb 20p 1 2 volt red, small pushfit 20p Mains neon, red, pushfit 16zp CAPACITOR GUIDE - maximum 500V - Up to .01 ceramic 2p. Up to .01 poly 3p. Up to 1000PF silver mica 5p. 1,200PF up to .01 Philips transformer, £1.50 silver mica 10p. .013 up to .25 poly etc. 4p. 2 1 2 Amp 250V A.C. rotary 16p safety fused. In 200- .27 up to .68 poly etc. 6p 1 2 Toggle lop 220-240v. Out 240v Over 500 volt order from above guide and few Wafer Rotary, all types 30p 60ma+6.3v la approx others listed below. 2" x 24" x 21" £1.50 6p..1 /600: 10p. .01/1000, S.P.S.T. 10 amp 240v. white rocker switch with 1/350, 8/20, .1/900, .22/900, 4/16. .25/250 AC (600vDC) .1/1500 neon. 1" square flush panel fitting 30p 40p. 5/150, 9/275AC, 10/150, 15/150, 40/150. PIANOKEY SWITCH UNIT POTS 5 lever, interlocking 2 pole mains -'- 3 pole 2 way Log or Lin carbon 12p TRIMMERS, 20p each + 3 of 6 pole 2 way 15p Switched 23p 100PF Ceramic, 30PF Beehive, 12PF PTFE Dual Pots 38p 2500PF 750 volt, 33PF MIN. AIR SPACED COMPUTER AND AUDIO BOARDS VARYING PANELS WITH ZENER, GOLD BOND, Dual Er switch 50p 5PF, MIN. AIR SPACED, 50PF CERAMIC. SILICON, GERMANIUM, LOW AND HIGH POWER Lin wirewound 25p CONNECTOR STRIP TRANSISTORS AND DIODES, HI STAB RESISTORS, Slider Pot 25p Belling Lee L1469, 4 way polythene. 3p each CAPACITORS, ELECTROLYTICS, TRIMPOTS, POT Dual Slider 35p CORES, CHOKES ETC. Strong grey plastic box same design as die cast 3Ib for 85p + 60p post and packing ali 44" x 24" x 1 4" .. 40p 7Ib for £1.75 + 80p post and packing 1" or 1 é" or ;" CAN CLIPS 2p THERMISTORS Skeleton Presets Clear Plastic Boxes Slider, horizontal or vertiFor component storage or VA1008, VA1034,) MAINS DROPPERS cal standard orsubmin.5p projects, sliding lid. 1r x VA1008, VA1034. 7p 36 + 79 ohm 20 p 1z"x1" lop VA1055, VA1066, 66+66+158 ohm, 66+66+137 ohm, VA1082, VA1100 ) 17+14+6 ohm, 266+14+193 ohm KNOBS 25p 10p 50+40+1k5 ohm SILVER METAL PUSH ON WITH POINTER, OR VA1077, WHITE PLASTIC, GRUB SCREW WITH POINTER AND VA1005, VA1026 15p 285+575+148+35 ohm 35p Y SILVER CENTRE 8p EACH. 25+35+97+59+30 ohm 1" DIAM. WITH 11" SKIRT SPUN ALUMINIUM GRUB SCREW FIXING, 1" 30p EACH. 54" x 22" Speaker, ex -equipment 3 ohm 30p RELAYS 2 Amp Suppression Choke 5p ZM1162A INDICATOR TUBE 12 volt S.P.C.O octal 3x24)(ye 1 PAXOLINE 0-9 Inline End View. Rectangular Envelope 170V 2p mercury wetted high 48 x x 2 5M/A J? 2 for 1 p â", £2.00 speed 75p 220K2 Et 100 ohm 3 watt resistors .. 4p RESETTABLE COUNTER P.O. 3000 type, 1,000 VALVE RETAINER CLIP, adjustable 2p English Numbering Machines LTD. OHM coil, 4 pole c/o MODEL 4436-159-989 60p OUTPUT TRANSFORMERS 6-14 volt, 6 digit, illuminated, fully enclosed. £2.50 12 volt d.p.c.o. heavy Sub-miniature Transistor Type 25p Ferric Chloride, Anhydrous mil. spec. 11b. bag 50p. duty octal Sop Valve type, centre tapped or straight 40p 2 Locking with 2 to 3 keys , - THEJOHNS RADIO SHACK BATTERSEA, LONDON 161 ST. HILL, Open 9.30 a.m. till 8 p.m. Monday to Saturday also Sunday afternoons S.W.11 Phone 01-223 5016 642 3 pin lead . din to open end, 11vd twin screened 35p Whiteley Stentorian 3 ohm constant impedance volume control way belowtrade at £1 Drive Cord 1 p per yd. RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com SEMICONDUCTORS Full spec. marked by Mullard. etc. Many other types in stock AC107 .. 14p BC178A/B .. 13p B F178/9 25p AC127/ 11p BC179B .. 14p 6E180/1/2/3 22p AC128/176 11p BC186/7 .. 20p BF184/5 15p ACY28 .. 18p BC213L .. 10p B F194/5/6/7 8p AD149 40p BC327/8 .. 19p BF194A 12p AD161 /2 matched pr. 69p BC337/8 .. 14p 8E200 .. 20p AF116/7 12p BC547/8 .. 11p B F262/3 23p AF124/6/7 20p BC558A .. 11p B F336 .. 25p AF139/178 .. 30p BCX20 .. .. 13p 6E528 Dual Mosfet 92p AF180/1 30p BCX32/36 .. 12p BFW10/11 F.E.T. 45p AF239 .. 20p BCY40 .. .. 60p BFX29/30 16p ASY27/73 .. 25p BCY70/1/2 .. 9p BFX84/88 16p BC107A or B 9p B D112/3/5/6 .. 50p B FY50/1 /2 11p BC107/8/9 .. 7p BD131 .. .. 30p BFY90 .. 50p BC108A/B/109B/C 10p BD132 .. .. 30p BR101 BC147/8/9 .. 7p BD135 .. .. 30p BRY39 Programmable30p Unj Junction 34p BC147A/B 8p B D201/2/3/4 .. £1.00 BRY56 34p BC148A/B, 9B/C/S 8p B 0232/4/5 49p BSV64 .. 40p BC157/8/9 .. 9p BDX77 .. £1.40 BSV79 F.E.T. .. £1 BC158A/B 11p BF115 .. 15p BSV80 F.E.T. .. 90p BC159B/C,157A 11p BF167/173 20p BSV81 Mosfet .. 90p BRIDGE RECTIFIERS Amp Volt Amp Volt 1,600 BYX10 30p 2 30 LT120 type 30p 1 140 OSHO1 -200 30p 0.6 110 EC433 15p .4 42 BY164 35p 5 400 Texas 75p . . . . . . . . . . . . . . . . 1 IN4004 IN4005 IN4006 IN4007 SR100 SR400 REC53A LT102 RECTIFIERS Amp Volt 1 400 600 800 1 1,000 5p 6p 7p 7p 7p 100 8p 400 14p 1,250 30 10p 40p 600 36p 300 45p 900 1,200 50p 600 34p 26p 300 40p 1,200 52p 40p 300 600 50p 900 60p 1,200 80p 150 35p 300 45p 500 55p 300 30p 600 65p 900 80p 1,200 95p 300 £2.00 400 £2.50 500 £2.75 600 £3.00 200 60p 300 £1.75 1,200 £2.50 1 1 1.5 1.5 1.5 2 BYX38-600 2.5 BYX38-300R 2.5 BYX38-900 2.5 BYX38-1200 2.5 BYX49-600 2.5 BYX49-300 2.5 BYX49-900 2.b BYX49-1200 2.5 BYX48-300 6 BYX48-600 6 BYX48-900 6 BYX48-1200 6 BYX72-150R 10 BYX72-300R 10 BYX72-500R 10 BYX42-300 10 BYX42-600 10 BYX42-900 10 BYX42-1200 10 BYX46-300* 15 BYX46-400* 15 BYX46-500° 15 BYX46-600* 15 BYX20-200 25 BYX52-300 40 BYX52-1200 40 *Avalanche type Parmeko 20H .12A potted choke 60p RG4-1250 Mercury vapour rectifier £5.00 1"Terryclips chrome finish .. Cinch 10 -way terminal block 4p 15p Pair of LA2407 Ferrox cores with adjuster Chrome Car Radio facia Rubber Car Radio gasket DLI Pal Delayline . . .. .. .. . Relay socket Take miniature 2PC0 relay B7G or B9A valve can .. 25p 15p 5p 80p 10p 2p 0-30, or 0-15, black pvc, 360° dial, silver digits, self adhesive, 4,1" dia. 10p OPTO ELECTRONICS ORP12 44p Photo transistor BPX40 65p BPX29 £1.00 BPX42 £1.50 OCP71 35p BPY10 £1.00 BIG L.E.D. 0.2" (VOLTIAC) 2v 50m/A max. B PY68 RED 15p BPY69 £1.00 ORANGE' BPY77 J r 16p GREEN Diodes YELLOW PHOTO SILICON CONTROLLED SWITCH BPX66 PNPN 10 amp £1.00 .. BSX21 . .. .. 13p 16p BU105/01 93p CV7042 (0C41 0C44, ASY63) 7p GET111 .. 40p 0C35 .. .. 34p ON222 30p TIS88A FET .. 33p ZTX300 11p 2N393/M A393.. 30p 2N706 .. .. 8p 2N987 .. .. 35p 2N2219 18p 2N2401 (ASY26-27) 20p 2N2904/5/6/7 .. 13p 2N2907A .. 15p 2N3053 .. 13p 2N3054 35p 2N3055 (or equiv.) 33p 2N3819 FET .. 16p 2N5036 .. 60p 40250 .. 60p . . . 6 25 25 Tested unmarked, or marked ample lead ex new equipment ACY17-20 8p 0071/2 5p ASZ20 8p 0C200-5 10p ASZ21 BC186 15p 11p BCY30-34 10p BCY70/1/2 8p BF115 10p BY127 8p BZY88 series 5p HG1005 2p HG5009 2p 2p HG5079 L78/9 2p M3 10p OA81 3p 0A47 2p 3p 0A200-2 0C23 20p TOTAL GOODS PLUS CARRIAGE, ADD V.A.T. TIC44 2G240 2G302 2G401 2N711 2N2926 2N598/9 2N1091 24p 2-50 6p 10p 25p 7p 6p 8p 8p 2N1302 2N1907 2-50 Germ. diode 1 p GET120 (AC128 in 1"sq. heat sink) 20p GET872 12p CA3001 R. Amp TAA300 1wt Amp NE555v Timer TAA550 Y or G TAA263 Amp SN7483 TTL F. 7400/10TTL Amp 1 1 1 6.5 10 15 6.5 6.5 20 15 30 BTX94-900 BTX94-1200 Volt .. 74p .. £5.00 .. £7.00 .. .. 240 BTX18-200 .. 400 BTX18-300 .. 240 BTX30-200 .. 500 8T102 -500R .. 700 BT106 .. .. 500 BT107 .. 500 BT101-500R .. 500 BT109-500R 600 BTW92-600RM 800 BTX95-800R Pulse Modulated 1000 28T10 (Less Nut) 50p 65p 40p 75p 85p £1.00 90p 75p £3.00 .. £10.00 £4.00 . 6p way Cinch standard 0.15 pitch edge socket 20p U.E.C.L. 10 way pin connector 2B6000 8 OA1 P10 U.E.C.L. 20 £1.00 £1.20 £1.00 £1.25 45p 40p 65p 80p 13p 14p £1.09 THYRISTORS 3.5mm Switched Socket T03 HEATSINK T=AA570 Plastic Coax 5 or 6 pin 240° din Speaker din switched Europlec HP1 TO3B individual 'curly' power transistor type. Ready drilled 20p TAD100 AMRF TRIACS Volt 400 900 1200 Car Aerial Philips Iron Thermostat 15p Bulgin 2 -pin flat plug and socket 10p McMurdo PP108 8 way edge plug 10p INTEGRATED CIRCUITS 741 8 pin d.i.l. op. Amp 23p ZN414 RX Amp volt .. 15p 2MFD 250 volt .. 20p CQY11 B L.E.D. 500 volt 10MFD .. 80p Infra red transmitter £1 4MFD 250 volt 20p One fifth of trade 150 volt 15MFD .. 50p Wire ended glass neons 5p METAL CHASSIS SOCKETS Plastic, Transistor or Diode' Holder 1p Transistor or Diode Pad 1 p Holdersorpads 5Opper1 00 OTHER DIODES IN916 .. .. 6p 1N4148 .. .. 3p BA145 .. 14p Centercel .. 10p BZY61 .. 10p 88110 B Varicap 20p BA182 24p 0A5/7/10 10p BZY88 Up to 33 volt 7p BZX61 11 volt .. 16p BR100 Diac. .. 19p 7401/2/4/20/30 .3" red 7 segment L.E.D. 14 PAPER BLOCK CONDENSER D.I.L. 0-9 D.P. display 1.9v, 0.25M FD 800 volt .. 30p 10m/a segment 73p 1 MFD 250 SMALL ORDERS, ENCLOSE SUITABLE STAMPED ADDRESSED ENVELOPE LARGE ORDERS, ADD SUFFICIENT FOR POSTAGE, INSURANCE, ETC. JUNE BSX20 10p way pin connector 2A60000A1 P20 20p U.E.C.L. 10 way pin socket 26606001 R10 10p U.E.C.L. 20 way pin. socket B 260800A1 R20 20p BELLING LEE L1354 TV Aerial diplexer 10p Philips electronic engineer kits add on series E1004 £1.00 each (parts worth more) . SOLDER Multicore - 2,p foot ENAM. COPPER WIRE SWG, PER YD. 18 3p 20-24 2p 26-42 1p GARRARD GCS23T Crystal Stereo Cartridge £1.00 HANDLES Rigid light blue nylon 6,1" with secret fitting screws 5p Rotor with neon indicator, as used in Seafarer, Pacific, Fairway depth finders 20p each Miniature Axial Lead Ferrite Choke formers 2p DEE PLUG McMurdo DA15P 15 way chassis plug 15p Fairway 18009 Coax. socket 3p TIE CLIPS Nylon self locking 7" or 3z" 2p CINCH 150 12 way edge socket 10p Mixed nuts, bolts, washers etc. 35p 11b MAIL ORDER CUSTOMERS ONLY ADD 8 V.A.T. 1975 643 www.americanradiohistory.com WILMSLOW AUDIO THE SPEAKERS Baker Group 25, 3, 8 or 15 ohm Baker Group 35, 3, 8 or 15 ohm Baker Group 50/12, 8 or 15 ohm Baker Deluxe 12", 8 or 15 ohm Baker Major 3, 8 or 15 ohm Baker Superb 8 or 15 ohm Baker Regent 8 or 15 ohm Firm for speakers! SPEAKERS SPEAKER KITS (Carr. 75p each. £1.50 pair) £31.95 Baker Major Module 3, 8 or 15 ohm each £10.75 £33.80 Goodmans Mezzo Twinkit pair £37.75 £43.98 Goodsmans DIN 20 4 ohm each £10.75 £11.00 £38.33 Helme XLK25 pair £9.50 £20.35 £32.40 Helme XLK30 pair £13.75 £14.50 £13.85 Helme XLK50 pair £8.00 £37.00 £31.45 Kefkit 1 Baker Auditorium 12" pair £13.00 £38.75 £14.75 Kefkit 3 Celestion PST8 (for Unilex) each £3.00 £34.00 £6.50 Peerless 3-15 (3 sp. system) Celestion G12H 8 or 15 ohm each £13.75 £13.90 £2.75 Peerless 20/2 Celestion G12M 8 or 15 ohm each £13.95 £11.15 £3.70 Peerless 30/2 Celestion G15C 8 or 15 ohm each £19.50 £22.25 Goodmans 81? 8 or 15 ohm Peerless 20/3 £5.10 Celestion G18C 8 or 15 ohm each £21.25 £30.55 Goodsmans 10P 8 or 15 ohm £5.40 Peerless 50.4 Celestion MF1000 8 or 15 ohm each £32.40 £10.95 Goodmans 12P 8 or 15 ohm £12.95 Richard Allan Twinkit EMI 13 x 8, 3, 8 or 15 ohm each £8.30 £2.10 Goodmans 12P -D 8 or 15 ohm £15.75 Richard Allan Triple 8 EMI 13 x 8, d/cone 3, 8 or 15 ohm each £12.75 £2.35 Goodmans 12P -G 8 or 15 ohm £14.75 Richard Allan Triple EMI 13 x 8 type 350, 8 or 15 ohm each £18.50 £7.65 Goodman 12AX 100 watt 8 or 15 ohm £33.75 Richard Allan Super Triple EMI 13 x 8 20 watt bass each £22.00 £6.15 Goodsmans 15AX 100 watt 8 or 15 ohm £37.25 Wharfedale Linton 2 kit EMI 5" 14A/730 mid -range 8 ohm pair £18.50 £2.80 Goodmans 15P 8 or 15 ohm £19.50 Wharfedale Glendale 3 kit EMI 61" 93850 4 or 8 ohm pair £32.50 £2.32 Goodmans 18P 8 or 15 ohm £33.50 Wharfedale Dovedale 3 kit EMI 8 x 5, cer. mag. 8 ohm pair £50.50 £1.65 Goodmans Hifax 750 £14.95 EMI 8 x 5, 10 watt, d/c roll/s 8 ohm £2.75 Goodmans Axent 100 tweeter & crossover £6.75 EMI 10 x 6 93870 8 ohm £2.15 Goodmans Audiom 100, 8 or 15 ohm PA/DISCO AMPLIFIERS (Carr. and ins. £1) £11.12 EMI 2'-," tweeter 8 ohm .62 Goodmans Axiom 401, 8 or 15 Baker Major 100 watt ohm £16.00 £46.00 Elac 9 x 5, 59RM109 15 ohm, Linear 30,40 Goodsmans Twinaxiom 8" 8 or 15 ohm £28.00 £8.11 59RM114 8 ohm £2.75 Goodsmans Twinaxiom 10" 8 or 15 Linear 40/60 ohm £32.50 £8.60 Elac 61" d/cone, roll surr. 8 ohm £3.25 Gauss 12" full range 8 ohm Linear 80/100 £65.00 £54.50 Elac 61" d/cone 8 ohm £2.50 Gauss 12" Bass 8 ohm Linear 100 watt slave £65.00 £40.75 Elac TW4 4" tweeter £1.40 Gauss 15" full range 8 ohm Eagle PRO A120, 120 watts RMS £120.00 E70.00 Elac 10" 10RM239 d/c 8 ohm £2.50 Gauss 15" Bass 8 ohm Eagle PRO A65, 65 watts RMS £70.00 £91.25 Elac 8" 3 ohm £2.30 Gauss 18" full range 8 ohm Eagle PRO A35, 35 watts RMS £71.00 Eagle Crossover 3, 8 or 16 ohm Eagles TPA40 mains/12v mobile Gauss 18" Bass 8 ohm £46.50 £75.00 Eagle CT5 cone tweeter 8 ohm £1.65 All the above Gauss Eagle HHS 36 watts. mobile 12v. (American) speakers are £34.75 Eagle CT10 tweeter 8 or 16 ohm £2.40 fitted with 4;" voice coils and can handle 200 watts Eagle TPA20 paging amplifier £41.75 Eagle DT33 dome tweeter 8 ohm £5.05 RMS. Eagle RA859 Reverb (p. & p. 75p) £16.90 Eagle FF5 3 way crossover £2.90 Kef T27 Eagle RA856 Reverb (p. & p. 75p) £11.60 £4.85 Eagle SN75 crossover with tw. control £3.75 Kef T15 £5.55 Eagle FF28 multicell, horn £7.28 Kef 8110 £6.70 Eagle HT15 horn tw. 16 ohm MICROPHONES (p. & p. 50p) £3.52 Kef B200 £7.60 Shure 515 SB Eagle HT21 horn tw. 8 ohm Low Impedance £5.45 Kef B139 £13.88 £13.00 Shure 515 Eagle MHT10 horn tw. 8 ohm SA High Impedance £3.55 Kef DN8 £14.60 £1.85 Shure 545 Dual Eagle FR4 4" full range Impedance £4.90 Kef DN12 £27.75 £4.60 Shure 588 SB Eagle FR65 6+" full range Low Impedance £7.70 Kef DN13 £18.50 £3.10 Shure Eagle FR8 8" full range 588 SA High Impedance £9.85 Richard Allan CG8T 8" d/c roll rurr. 8 £19.00 ohms £5.90 Fane Pop 15 watt 12" £4.85 STC 4001G super tweeter £5.25 FREE with Fane Pop 257 30 watt 12" loudspeaker orders over £7 £6.95 2a" 64 ohm, 70mm 8 ohm, 70mm 80 ohm .62 Fane Pop watt 12" "HiFi Loudspeaker Enclosures" book £11.15 2;" 75 ohm .47 Fane Pop 55 12" 60 watt £12.00 7" x 4" 3, 8 or 15 ohm All items guaranteed new and perfect £1.30 Fane Pop 60 watt 15" £12.75 8" x 5" 3, 8 or 15 ohm £1.40 Fane Pop 100 watt 18" £24.00 10" x 6" 6, 8 or 15 ohm Prompt despatch £2.15 £8.00 £9.50 £13.00 Fane Crescendo 12A 8 or 15 ohm Fane Crescendo 12B 8 or 15 ohm Fane Crescendo 15, 8 or 15 ohm Fane Crescendo 18, 8 or 15 ohm Fane 701 twin ribbon horn Fane 910 horn Fane 920 horn Fane 152/12a 15" 15 ohm Fane 801T 8" d/cone roll surr. Fane 808T 8" cl/cone Fane 807T 8" d/cone roll surr. The Ultimate Radio! GRUNDIG SATELLIT 2000 I. I = I- o n 1 II g I 10 _ I Our Price £149.95 inc. Carr. & ins WILMSLOW AUDIO, PLUS VAT AT 25% Send stamp Big for free booklet `Choosing discounts f on Grundig, ITT, Send stamp for list a speaker' Koyo, etc. :s:::::: ;i =:-.-: éiiyii i .i.í ; WILMSLOW ...ii.iii AUDIO ii . . . ; i;Ce> i:Oi - You've got your yacht, private aircraft, Rolls Comiche? then all you need fora full set of status symbols is this latest model Grundig Satellit. Germany's top radio! Radio performance, appearance and sound quality are all superb. VHF/FM, MW, LW 10 SW bands plus bandspread, 27 transistors and 22 diodes, Battery/Mains (110/240v.), 2 ,speakers, 57" telescopic aerial. Big discounts on Grundig, ITT, Koyo, etc. Send stamp for list. !r uiii iir::.i Carriage: 38p per speaker 12" and up 50p each, 25p per tweeter, crossover or2;",70mm speaker kits 75p each (£1.50 pair) II - ' . ., = . ,. . - . ' . - . DEPT RC - 0' ..._ SWAN STREET, WILMSLOW, CHESHIRE 644 LOUDSPEAKERS: SWAN WORKS BANK SQUARE, WILMSLOW, CHESHIRE 10 AMPLIFIERS, RADIO ETC. SWAN ST., WILMSLOW, CHESHIRE RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com - r EL ECTRO A CATALOGUE 7 "I MADE IT MYSELF" Imagine the thrill you'll feel ! Imagine how impressed people will be when they're hearing a programme on a modern radio you made yourself. \ ISSUE Now! Learn the secrets of radio and electronics by building your own modern transistor radio! Cata\ (] 1 1ee9,a,ea eomD°ie" P: MaSe,a15 labi es t:w'°ae°p,a9a m5 otne to a What new, better -paid career! No dreary ploughing through page after page of dull facts and figures. With this fascinating Technatron Course, you learn by building! No soldering - yet you learn faster than you ever dreamed possible. Yes! Faster than you can imagine, you pick up the technical know how you need. 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And after the course you can go on to acquire highpowered technical qualifications, because out famous courses go right up to Cit> & Guilds levels. Send now for FREE 76 page book - see how easy it is - read what others say! Find out more now! This is the gateway to a thrilling new career, or a wonderful hobby you'll enjoy for years. Send the coupon now. There's no obligation. including 25p Refund Voucher ISSUE 3 SemcoduFESTRIPLE 66.bil IIl'NA511(' .SI(1XA1. 0 E:11' 1.1130' ('1191'. PROF. SHIFT REGISTER E00R 3166 TYPE N.Í. 5 481 1-24 liship. Cnmprkes 11011.1 66.1,11 2 II dynainie shift '1'811 14 pin type 33P Í 30P 27P registers lth in.h.pendrll inputs and 0111. '1'81116 38p 35p 32p puts. 7"11, rrnnpalil1ility and Indiered 1111,1 1.11\1' Í'11S'!' X. lins 100 nduy1 Ilu enp0 r 10(111 3111 0rí BPS 14 16p 14p 12p at r (he el. 0rk pí1 A bout .stra pl.ri '.iodOr 1311 111 17p 13p 15p insurl a full 10ng í,,t Ili'' nul put. Í11'S 8 spin 1y(1' 1Sp 13p Ilp 1 2X308 2X3843 13(29 0.22 £1.35 0-127" 31311 391. 1..E_11.7` All in01icat0 irr 0,9 I loci 11í11l p00í111. 211417 0.11 0.16 0.16 0.17 0.17 0.28 0.17 0.17 0.17 0.17 0.22 0.22 0.22 0.28 0.28 1028 113'1'121) VOLTAGE REGULATORS TO.3 Plastic 1-5 Antpe :..\.7015'1.129 5V (001d, In 3015F 0.11 oC71 (1126 0.31 0.31 411' ..\.7812 1,I3) 12V (Eynir. 0070 (325 '('I(Í)221 7'1141.\ '1'11423 'I'1843 100 0.15 0.16 0.16 0.16 0.16 0.16 0.30 0.15 0.30 0.70 0.15 0.45 0.45 0.45 1(10,132 045 111`24 0.21 311'1102 311'1104 25 217301) 11('2) 0C22 1/023 - Prive 0.39 0.39 0.22 0.18 0.20 0.18 0.18 0.13 0.19 0.19 0.33 0.18 0.18 0.18 0.33 0.33 0.28 0.39 Type 0.41 0.39 0.70 0.52 0.54 0.62 0.42 0.32 0.55 0.55 0.46 0.55 0.22 0.27 0.17 0.14 11('19 3131101 91.1111955 11.1E_1kw7 51.3121440 I 019311 Poire 111'1105. 0.30 0.44 0.13 0.13 0.16 0.16 0.50 £1.05 0.50 0.66 0.94 0.61 0.61 0.39 0.33 0.88 0.39 0.39 0.66 0.30 0.24 0.33 0.24 0.27 0.24 0.22 0.22 0.22 0.19 0.17 0.17 0.17 0.17 0.17 0.17 0.17 0.20 0.20 9I\'í'11)1 Price Type Type Prier 31187 1110$ 0.44 0.50 0.55 110) + x_711! X Type 1{0135 811130 130137 1(0130 µ01391 DTL 930 SERIES LOGIC I.C's Price Type No. X1:5: 0.21 0.21 0.21 13('170 13('170 11(113 13('1511 301621311') 0.75 BRAND NEW FULLY GUARANTEED DEVICES Prier Price 0.22 0.20 0.22 0.32 0.13 0.19 0.19 0.20 0.20 0.16 0.16 0.16 0.20 0.32 0.20 0.29 0.17 0.22 0.22 0.22 0.27 0.22 0.22 0.22 0.27 0.16 0.22 0.27 r71. 7422 742:) 74'!5 74211 742_ 7428 7430 7432 7437 7437 7430 7440 7441 7442 7443 7444 7445 744(1 7447 0.15 0.15 0.15 0.15 0.IS 915 0.39 0.39 0.25 0.25 0.15 0.25 0.28 0.32 0.30 0.30 0.15 0.30 0.40 0.40 0.40 0.40 0.45 0.15 0.40 0.42 0.35 0.35 0.15 0.74 0.74 £1.20 £1.20 £1.60 £1.20 £1.10 0.14 0.14 0.14 0.14 0.14 0.14 0.34 0.34 0.24 0.24 0.14 0.24 0.27 0.31 0.29 0.29 0.14 0.29 0.39 0.39 0.38 0.38 0.42 0.14 0.39 0.40 0.32 0.32 0.14 0.71 0.71 £1.15 £1.15 £1.55 £1.15 £1.07 Quantities Type 199 0.13 0.13 0.13 0.13 0.13 0.13 0.31 0.31 0.23 0.23 0.13 0.23 0.26 0.30 0.28 0.28 0.13 0.28 0.38 0.39 0.36 0.36 0.40 0.13 0.36 0.38 0.30 0.30 0.13 0.64 0.64 £1.10 £1.10 £1.50 £1.10 £1.05 1 7448 74.511 £1.10 0.15 7451 0.I5 7453 7454 7460 7470 7472 747:1 0.15 0.15 0.15 0.32 0.32 0.41 7474 0.41 747( 0.60 0.44 0.60 £1.10 0.90 £1.20 £1.00 £1.60 0.35 £4.00 0.65 £1.10 0.74 0.74 0.85 0.85 0.96 £1.50 0.60 0.60 0.44 0.60 0.90 £1.00 £1.50 0.50 7471) 7480 7481 7482 7483 7484 7485 748(1 7489 7418 7491 74!3_ 7493 7494 7415 7490 74118) 74104 741115 74107 74110 74111 74118 74119 74121 25 £1.07 0.14 0.14 0.14 0.14 0.14 0.29 0.29 0.39 0.39 0.58 0.43 0.58 £1.05 0.85 £1.15 0.97 £1.55 0.34 £3.75 0.63 £1.05 0.71 0.71 0.82 0.82 0.93 £1.45 0.58 0.58 0.42 0.55 0.88 0.95 £1.40 0.48 Quantities Type 100 + £1.05 0.13 0.13 0.13 0.13 0.13 0.27 0.27 0.35 0.35 0.56 0.42 0.55 £1.00 0.90 £1.05 0.95 £1.50 0.33 £3.50 0.60 £1.00 0.64 0.64 0.75 0.75 0.86 £1.40 0.55 0.55 0.40 0.50 0.85 0.90 £1.30 0.45 25 74122 74123 74141 74145 74150 74151 74153 74154 7415.5 74156 74157 74160 74161 74162 74163 74164 74165 '4106 74174 74175 74176 74177 74180 74181 74182 74184 74190 74191 74192 74193 74194 74195 74196 74197 74198 74199 0.70 0.75 0.85 £1.30 £1.50 £1.10 £1.00 £1.70 £1.20 £1.20 £1.00 £1.40 £1.40 £1.40 £1.40 £1.80 £1.80 £1.00 £1.60 £1.10 £1.25 £1.25 £1.25 £3.95 £1.25 £1.80 £1.95 £1.95 £1.95 £1.95 £1.30 £1.10 £1.20 £1.20 £2.75 £2.50 0.68 0.73 0.82 £1.25 £1.40 £1.05 0.95 £1.65 £1.15 £1.15 0.95 £1.35 £1.35 £1.35 £1.35 £1.75 £1.75 £1.55 £1.55 £1.05 £1.20 £1.20 £1.20 £3.85 £1.20 £1.75 £1.90 £1.90 £1.90 £1.90 £1.25 £1.05 £1.15 £1.15 £2.70 £2.40 100 t 0.65 0.70 0.79 £1.20 £1.30 £1.00 0.90 £I.60 £1.10 £1.10 0.90 £1.30 £1.30 £1.30 £1.80 £1.70 £1.70 £1.50 £1.50 £1.00 £1.15 £1.15 £1.15 £3.75 £1.15 £1.70 £1.85 £1.85 £1.85 £1.85 £1.20 £1.00 £1.10 £1.10 £2.65 £2.30 DEVICES 51.11 BE 511X E1Í TO QI'ALIFY FOR QUANTITY PRICE. (TTL 74 SERIES ONLY) DATA IS AVAILABLE FOR THE ABOVE SERIES OF (.COs IN BOOKLET FORM. PRICE 35p. RADIO & ELECTRONICS CONSTRUCTOR 646 www.americanradiohistory.com -the lowest prices! NEW TEXAS TRANSISTORS BRAND GERM. Coded and Guaranteed ,:l(1"l'. n'71 21:571:1 l'nk l'I Iv I8"5 111:174 110I0 1/I21e1 21::181'1' 11011 21::182l' 111'82 'l':t 2(:34411 (1'44 21:34511 18'45 'Df 'I. SILICON SWITCHING TRANS. TO -14 AIM. TO 2N706 8. BAY -27 28 95A. II u.al.I,. ,I,..ir,.. 80 00404 r .14m1 entail,. ALA" AVAILABLE in PN I' Srnt. ^N 2960. R1'V70. 1VI0-11 01.:: ml.a mite lire. fenv,n NPN or PN I. 'Ive -1.10 .011 120 55p n,cl, 1mk 50 For For For For Ime Him NIXIE DRIVER TRANSISTOR Suitably replacement £ p 0,5.5 1.10 1,92 Mur 2(.378 (878 21:399A 2N(302 211417 .1F117 T8 ND C.F.NF.RSL PURPOSE NPN 8.25 14.30 SIL. G.P. DIODES all (10 500 :Osn/olV for BOX 21, 1' 407, 2N 1893 1201,14 25 I Ils)+ 0.17 0,19 0,16 40PIVIMin.l Sub -Min. Fn11 1,000 Pak No. 1! I 211 (( 2 III 1( :4 4 U4 Q 5 4 1( li " 7 4 1/ 8 4 (( ( !1 7 4,404 7 ()II - 30W.hfc= 35-170. Replaces the majority 01 Germanium posa -r transistors in the OK'. AD and NKT range. Ils' 25 0,47 0,44 BDY 2(1. 1 0.55 25 IW- 0.53 0.51 NEW 9th EDITION Over pages TRANSISTOR EQUIVALENTS BOOK. A complete cross reference and equivabook for lents European, American and Japanese Transistors/ Exclusive to RI. PAK £2,30'each. 300 LARGE RANGE OF TECHNICAL AND DATA BOOKS ARE NOW AVAILABLE EX. STOCK. SENI) FOR FREE LIST, A 111'77 0.:4 l'NI' .. type Imoi+tnrs lnalsi+tors(3'44,'4:5;81,810 18'751mnsi4orv .. .. .. 111-72 transistors AC128 transistor. l'NI' high gain .. 5C'l26 transistors l'NI' .. .. 0(51 Irin< (ean,inlnea .. -. 1371 type Iransistom .11'127 124 Complementary pair. 1h0 eked l'NI' N('N .. 1(1:1 :l A8'11a type transistors .1F117 type transistors QI4 3 I1C171 1(15 7 2N2t126 Q17 918 Q2I (r=2 AD161/162 51 Q23 l('24 (' ('11511' GERM TRANS. OUR LOWEST PRICE 0F 75p ('ER P.41/f. Q'25 Q211 Q27 Q29 LOOK FOR OUR ADVERTISEMENTS PRACTICAL WIRELESS EVERYDAY ELECTRONICS AND RADIO CONSTRUCTOR FULL RANGE OF ZENER DIODES VOLTAGE RANCE 2-33V, 41100IV (00-7 Case) 9p ,m 111V ('Cop.Hatl l8p en. (01\' (50-10 Stud) 32p ea. .. 3 M.11YC'S 2x31A'C lut & . Q02 :1 l(:i:i 3 11:14 7 snitch Iransist,rs Silicon Silicon NI'N Inmsisnon 2N1711 .. Silkonl NPN transistors 2N2:100, 51031Hz (colo P397) .. Silicon 1'NI' 'l'11-5. 2.2N218µ & . ((:kl 3 x2N2!Ilui .. 2536411T'll-IS pinstir 30051Ha NPN 2N31153 NI'N Silicon transistors PNI' transìstots 3x2X37U3. 2:-2N3702 ... .. .. .. 1 Q:46 Q:47 :1 938 7 555 2 511 U 3 75 t' 0.54 0.54 U :8l 60 I" li 311 4 L' 16 7 Al V 0.54 0.54 0.54 Cla 10 217 301 1'18 8 0.54 l'19 20 !1 20 ('10 9( 2n 211 1'13 :01 CIA 1501 L"15 211 t'_w 13 0.54 L:21 30 0.54 U2:1 25 U24 20 0.54 0.54 1'25 25 V211 :00 0.54 ('29 10 U32 25 U33 15 C34 301 1'35 25 1.ta 20 U37 U:18 30 21 U39 30 0.34 0.54 0.54 0.54 LC, 65p each MAMMOTH I.C. PACK APPROXIMATELY 200 PIECES ASSORTED MANUFACTURERS FALL-OUT INTEGRATED CIRCUITS INCLUDING LOGIC 74 SERIES LINEAR and AUDIO AMPLIFIERS MANY CODED also SOME UNKNOWN TYPES -YOU TO IDENTIFY PAK NO. M.I.C. 200 PRICE £1.25 per PAK including p & p & V.A.T. 1973 CATALOGUE NOW READY 10p INTEGRATED CIRCUIT PARS Description U 8 NI'N l'NI' S/ieon transistors 2x231131. satisfied Price £p 120 Glens Sob -Min. General Purpose Germanimn Diodes 1 2N7104. if not Pak 'No. t 1 II Money back refund 0.54 0,54 0.54 0.54 0.54 0,54 0.54 NI'N ((31 SUPER PARS N SEMICONDUCTORS D U 1xMAT Unequalled Value and Quality KING OF THE PARS 0.54 0.54 0.54 0,54 0.54 . 03'44 Germanium tranaiswn:L.F.-. A(127 NPN (1en1100um transistors NKT transistors :1.F. R.F. ended .. 10 052112 Silicon diodes aah.min. ,. 8 11.181 diodes 1.5 176914 Silicon diodes 751'1V 75m.\.. 8 0,195 Germanium diodes soh.min IX1i9 IOA PIV Silicon rectifiers 154258 .. Silicon power rectifiers BVZ13 4 Silicon transistors 2 x2N090, x 2X997. x2N(i!OI 7 .Silk snitch uitch transistors SN7111 4 4 1 Q311 AUDIO Er ELECTRONIC COMPONENTS .. 4 120 Q(9 .. H.F. type transistors Sil. Epoxy transistors :nixed colours NI'N 2 .ST'.141 A 3 x S'l'.140 M:VOT"S 2x315T RIO A 2. MAT ' 0.34 0,54 0.34 0.54 0.54 0.54 0.54 . :1 Q'20 0.40 CP 300 T03 METAL CASE SILICON Vebo = (00V. Veen = 60V I.C. = 15 mops. Pint = (151V. hfe = 2(1. IIOIfT'.= 1518e. Suitably replacmrnt for 2N 3055. BIIV II or 2 0.54 0.54 Q12 (K8 GP 100 T03 METAL CASE GERMANIUM Vebo = 88V. Vee., = 510'. I.C. = 10 amps. Mot ' Priee Red spot transistor l'NI'.. White sledÍ R. F. transttors Ideal for Organ Builders. Sit trans. suitable for PE Organ. Metal 7'o-18 Egot. 'ZTX3011 Op each. Any Qty. T,'ed £p 0.55 1,65 5.50 9.90 QUALITY TESTED SEMICONDUCTORS ('4u 10 U43 U44 23 20 1346 7 U41i 20 1147 10 1:48 12 U411 .. Mixed Germanium Transistor, SF'/RP .. .. .. (Irnminium Gold Bonded Sub -Min. like 053, 0547 ., .. Germanium Tmnsislom like (ICO1. AC128 .. .. 210005 Sub -Min. Silicon Dieales .. .. .. ... .. .. Sil. Planar 'Un,ns. NPN like B)l'!k7A, 2767016 .. .. Sil. Rectifiers '('01'.11 ST 750,45 VLTG. RANGE up to 1000 Mil. Planar Diodes DU-7 Glass 251141.1 like 0:1200202 .. Mixed Voltages, 1 ll'att Zoner Diodes .. BSV50 charge storage Diode. 1)U-7 Glass .. .. ('NI' Ail. Planar Trans. TU -S like 2X1132, 23:2984 .. PNI'.Nl'N Sil. 'l'ranvstois 13(:901 A 2S 11µ .. .. )Iixe,l Silicon and Germanium Diodes .. .. .. N l'N Ail. Planar Tram. u,,. 'f0.5 like I(FAS I, 23607 .. .. 3 .imp Silicon/ Redìliers Stud Type up to (000PIV .. ,. Germanium ('NP AF Transistors TO -3 like :ICY 17-22 .. li Amp Silicon Rectifiers BYZI3 Type up to 600 PIV .. .. NPN Transistors like 13;1001 Silicon .. .. 1.5 Amp Silicon Rectifiers Top Hat up to IOW PIV .. .. AF. (crmanimn Alloy Transistors 20300 Scrim & ((C71 .. .. 315DT's like 318e Syrien, PXP Transistors .. Cermmd,on I Amp Rectifiers G131 Series up to 300 PLY .. :005tH, NPN Silicon '('ro40istors 2X708, I(SY27 .. Fast Switching Silicon (Ii,slas like 1X014 Micro-)lin. .. .. Amp S('R's TO -5 ea,. up to (9x1 PIV CR31/25-000 .. .. Zeiler Diodes 4(1101W 00.7 case 3-I8 volts mixed iv I Amp RenliSero 1X41810 Series Plusl Case Silicon .. Silicon l'NI' Alloy Trans. TO -5 BCY26 2030214 .. Silica Planar 'l'mnsistorn ('NP TO -18 2N21(06 .. Silicon Planar NPN Transistors TO.5 BF1750/51152 Silicon Alloy Transistors SO -2 PNP 110200, 2S322 .. Fust Switching Silicon Trans. NPN 40051110 283011 .. .. RF. Germ. ('NI''l'reinsi,tors 2N1303í5'1'0 .5 -. .. .. .. .. I)unl Tronsistors 6 lead 'l'U -5 2N20iO .. .. .. Sil. Trans. Plastic TU -l8 5,F', BC1(311(4 .. I -. .. .. Sit Trans. Plastic TO -5 BC115(110 .. .. .. 35 SCR. TO66 Igo to lSnl'(V Uoijnnrtion trnnsiotoro similar to TI043 T112211,(9 plastic triers 50V SA .. .. .. .. NI'X Oil. power transistors like 2831156 SPX Sil. plastic power trans. 19ßV like 2763.204(5201: .. ... , . . 1 0.54 0.34 0,54 0.54 0.34 0.54 0.34 0.54 0,54 0.54 0.54 0.54 0.54 0.54 0,54 0.54 0.54 0.54 0.54 0.54 0,54 0.54 0.54 0.34 £1,08 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 0.54 £1,08 0,54 £1.08 £1.08 £1.08 Nos. mentioned al ive Ore given an a guide to the type of devise in the pork. The devices themselves are normally unmarked. (leak. FREE One 55p Pak of choice free your own with orders valued £4 or over, CADMIUM CELLS ORP12 48p SIL. RESTS. TESTED PIC 300m573h45 IA 1,5A 3A 341 005 II.I81 1764001 0.05 0.08 0,15 VII Il05 11.07 I 7640(2 0.06 0.10 0.17 210 I1J0: 0.10 1X40113 0,07 0.12 0.22 0.15 18404 (90 0.09 0.17 13141003 4141 8101 11801 11.08 11.12 - 11.19 0.14 0.30 0.08 0.15 0.30 0.10 0.18 0,35 184000 0.11 0.20 0,38 1X4007 0.12 0.25 0.48 0.30 0.58 - 10A 30.. 0.21 0.23 0.25 0.38 0,45 0.56 0.65 0.75 0.80 0.76 £1.00 £1.36 £150 £2.10 £2.60 Manufacturers' "Fall Outs" which include Functional and Part Functional Uits. These' £3.00 1200 0.3.5 re classed as 'o t-onvpec' from the maker's very rigid specification but an. idea for NEW LOW PRICED TESTED S.C.R' learning about 1.C,'a and experimental work. DIACS l'IV IA 3A 5A 5A 7A IVA IDA 305 TRIACS Pak No. Contents Price Pak No, Contents FOR USE WITH TRIALS Price Pak No. Contents T05C060111316T1164T048 T048 TIHB T048 Price SA 10:1 VBO5I2:1 11111(0 10321 25p each 50 (1.211 0.28 0.39 0.39 0.52 0.55 0.59 £127 U1C00=12x7400 TO.5 TO -66 TO -4b 0.54 l'IC-16=5x7440 0,54 l'IC30- 5<7490 0.54 IW 0.28 0.37 052 II52 0,55 0.64 0.70 £I.54 UIC01=1.2x7401 £ £ £ 0,64 1.1C480557448 0.51 ('11111 -Sr 7491 0.54 2101 IO amp POTTED 0.41 44:4 11,54 11.63 0.311 0.83 £1.711 0.67 UICO2=12x740? 0.54 l'ICSO =(2x7450 0.54 1'01 0.33 0.55 0.83 (' IC312 S-,74!12 0.54 BRIDGE RECTIFIER 41X1 048 612 II.6ï2 0.62 (1.74 0.8:1 £1,03 £1.03 U1CO3=12x74113 0,54 Ú1C:51 -12x2451 20 0,51 0,65 0.00 0.99 1'1(31:1=5x749:1 0,54 sink. Ixxl on heat 0.50 003 0.75 075 0.85 £1.07 £1.38 U1004=12x7404 0.64 LIC53=12x74.53 1.21 0.54 400 0.77 0.83 1'5)94=5x7494 0.54 100PIV. 99p each XOII 0.70 11.77 0N4 0.88 099 51.32 £115 8440 U1006=12 x740.5 0.54 L'1054=1257451 0.54 1'112U -5 x7495 0,54 1J1C00=8 x7406 0.34 UIC60=12 x 745u 0.54 210316 =5 x7496 0.54 131007=8 x7407 0.54 UIC70=8x7470 0.54 L'IC1011-3x74100 0,54 Giro No. 388-%000 All prices quoted m new pence UIC10=12x7410 0.54 l,'I1772=8x7472 0,54 U1C121=5x74121 0.54 UIC20=1.2 x7420 0.54 ('1C73=807473 0,54 l'IC141=5x74141 0.54 Please send all orders da reef to ware tons and despatch department 131C30=12 x7430 0.54 UIC74=.8x7474 0.54 L1C151=5x74151 0.54 U1C40=12x7440 0.54 U1C76=857476 0.54 UIC154-5x74134 0,54 UIC41=5 x7441 054 121C80-507400 0.34 UIC193=5074113 0.54 WATT 1L UIC42=5x7442 0.54 UIC81-5x7481 0.54 L'IC199==5 x74110 0.54 U1C43=507443 POWER NPN 0,54 131(302=5x7482 0.54 UIC44=5x7444 0.54 UIC83=5x7483 0.54 45p E11'H UICXI=25 Aa-s,rlod , - B/-PA/ff 2N3055115 U1046=5x7445 0.54 U1C80=5x7486 0.54 74's £1.65 Peke cannot bu split, but 25 assorted pieces (our mix) is available as PAK UIC Y Amp. BRIDGE RECOS. 50 v RMS 100 v ß51S 200 v 8315 35p each 4lp 45p 400v RMS 1000 e 1251S Size 16 rem UNE 55p x 16 mn,. LINEAR INTEGRATED CIRCUIT PAKS Manufait neri (all-out. DI699 NPN SILICON DUAL TRANSISTOR (Similar to 2X2060( 0.28 Xl, ULILi(xl 100+ 0,26 0.23 ULI(741 CLIC747 ULIC748 --- 19.- (:LIC71O 25 7 5 7 7189 .. 7W .. 741 .. 747 748 .. .. P.O. BOX 6, WARE HERTS e .. .. .. .,. 0.54 Postage and packing add 2Op. Overseas add extra for airmail. Minimum order 5Op. Cash with order please. Guaranteed Satisfaction or Money Back 647 1975 www.americanradiohistory.com ;t7T4 The International Audio Visual Aids Exhibition THE NATIONAL HALL, OLYMPIA, LONDON July 8th 11th 1975 - INTER NAVEX 75 is being held under the auspices of the EFVA/NCAVAE and organised by Brintex Exhibitions Ltd. 178/202 Great Portland Street, London W1N INTER NAVEX 75 Exhibits 6Nii. will include: Audio -Visual Presentations Audio -Visual Programmes Audio Equipment CCTV and Broadcast Television Equipment Cameras (Cine Et Photographic) Cassette Players (Audio) Filmstrips Flannelgraphs Er Services Index (transparencies) Information Services Language and Learning Laboratories Language Teaching Materials Cassette Teleplayers Cassette (Audio) Cassettes (Video Programmes) Cassette Et Tape Duplicators Cleaning Aerosols Et Solvents Lettering Libraries Copying Et Duplicating Courses Drawing Et Display Materials Editing Er Film Inspection Machines Episcopes/Diascopes Equipment Et Materials Advice and Service Centres Fade/Dissolve Projection Devices Film Loops Et Projectors Film Projection Accessories Films Filmstrip Projectors Lenses Magnetic Boards Magnetic Tapes (Audio) Markerboards and Chalkboards Micro/Macro-Projectors Multi -Media Kits Overhead Projectors Overhead Transparencies Materials Et Photography Planetarium Programmed Learning Projectors (8 mm) Projectors (16 mm) Publications and Literature Public Address Equipmen Radio Receivers Rear Projectors Record Players Records and Recorded Tapes Screens Slide Cabinets and Storage Slide Projectors Slides and Transparencies Stereoscopic Equipment Et Material Synchronisers (Sound/Vision) Taperecorders and Players (Audio) Tapes for Audio Systems Teaching Machine Et Systems Teleplayers Television Receivers for schools Training Services and Information Transparency Makers Trolleys and Stands Video Discs Video Projector Video Recorders and Tapes Viewers and Viewing Equipment Wallcharts and Flip Charts EXHIBITION HOURS: Tuesday, 8th July Wednesday, 9th July 9.30 a.m. to 6.00 p.m. 9.30 a.m. to 6.00 p.m. Thursday, 10th July Friday, 11th July 648 9.30 a.m. to 6.00 p.m. 9.30 a.m. to 4.00 p.m. RADIO & ELECTRONI'CS CONSTRUCTOR www.americanradiohistory.com CHINAGLLL\ PROFESSIONAL QUALITY TEST EQUIPMENT WITH ROBUST CLASS 1.5 PRECISION MOVEMENT ACCURACY 2.5% D.C. AND 3.5%A.C. 2 MONTH GUARANTEE SELF -POWERED AND POCKET -SIZED OPTIONAL 30kV.D.C. PROBE 33 RANGES 20k S2 /V d.c. 4k.S2 /V a.c. 1 PRICE £16.30 Inc. VAT (P. & P. 80p) PROBE £8.80 For details of this and the many other exciting instruments in the Chinaglia range, including multimeters, component measuring, automotive and electronic instruments please write or telephone: D TRADE ENQUIRIES WELCOMED IINAGLIA (U.K.) !JD. I. Understand electronics. Step by step, we take you through all the fundamentals of electronics and show you how easily the subject can be mastered using our 19 Mulberry6DZ WalkTel: London SW3 01-, 352 1 897 radio amateur. Learn how to become a radioamateur in contact with the whole world. We give skilled preparation for.the G.P.O. licence. unique Lerna-Kit course. {2} Build an oscilloscope. Read, draw and understand (3) circuit diagrams. Carry out over 40 experi- (1) ments on basic electronic circuits and see how they work. Do - - - - -- - - - -- - - - - -- - - - - - - - - - - - - - Brochure, without obligation to: BRITISH NATIONAL RADIO & ELECTRONICS SCHOOL, Dept AX 675 MI 1 P.O. Box 156, Jersey, Channel Islands. NAME ADDRESS ----MAW -.-----NMM_M---O--w all JUNE 1975 www.americanradiohistory.com ----- I Mil MI- Block caps please MIR Mil -InMI649 THE MODERN BOOK CO WORLD RADIO TV HANDBOOK 1975 A Complete Directory of International Radio Er TV Price: £3.85 110 OPERATIONAL AMPLIFIER PROJECTS FOR THE HOME CONSTRUCTOR by R. M. Marston PRICE £1.95 THE RADIO AMATEUR'S HANDBOOK 1975 by A.R.R.L. PRICE HOW TO GET THE BEST OUT OF YOUR BASIC MATH COURSE FOR ELECTRONICS TAPE RECORDER by P. J. Guy PRICE by H. Jacobowitz PRICE £1.65 BEGINNER'S GUIDE TO ELECTRONICS HANDBOOK OF IC CIRCUIT PROJECTS by T. L. Squires PRICE by J. Ashe PRICE £1.65 COLOUR T.V. WITH PARTICULAR THE AUDIO HANDBOOK REFERENCE TO THE PAL SYSTEM by G. J. King PRICE £5.30 by G. N. Patchett PRICE UNDERSTANDING Er USING THE RADIO SERVICING POCKET BOOK OSCILLOSCOPE by C. Hallmark PRICE £1.95 by V. Capel PRICE COLOUR TELEVISION SERVICING STEREO F.M. RADIO HANDBOOK by G. J. King PRICE £4.85 by P. Harvey PRICE ESSENTIAL FORMULAE FOR ELECTRONIC Er 110 SEMICONDUCTOR PROJECTS ELECTRICAL ENGINEERS FOR THE HOME CONSTRUCTOR by N. M. Morris PRICE £1.05 by R. M. Marston PRICE TOWERS' INTERNATIONAL TRANSISTOR FIRST STEPS IN TELEVISION SELECTOR by T. D. Towers PRICE £3.30 by B. Sexton PRICE WORKING WITH THE OSCILLOSCOPE THE PRACTICAL AERIAL HANDBOOK by A. C. W. Saunders PRICE £1.75 by G. J. King PRICE ALL PRICES INCLUDE POSTAGE £3.70 £1.70 £2.15 £5.25 £2.20 £2.75 £1.35 £4.75 £3.05 We have the Finest Selection of English and American Radio Books in the Country 19-21 PRAED STREET (Dept RC) LONDON W2 INP Telephone 01-723 4185 LATEST BOUND VOLUME No. 27 of "Radio & Electronics Constructor" FOR YOUR LIBRARY Comprising 772 pages inc. index PRICE £2.40 P&P 50p AUGUST 1973 to JULY 1974 BOUND VOLUME No. 25 (August 1971 to July 1972) BOUND VOLUME No. 26 (August 1972 to July 1973) PRICE PRICE Limited number of these volumes still available £2.00 £2.10 p. Et p. 50p p. Et p. 50p We regret all earlier volumes are now completely sold. out. Available only from r DATA PUBLICATIONS LTD., 57 MAIDA VALE, LONDON, W9 1SN 650 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com eeo Qp,P ßGO ,\;3.-\;!\!\.395\-- e\`' 2 P 22' P\GS ( ' \s \G GN\NSP G ON P \ 12. ß\GNe ß \ E \50XpM 15. ,NNM0 Qß O 16. -( Pe SS P \.\\'. G Pp pG\ `' NS P 0E- P-GNS GSS P O \QS 'SG QOß\SNSp \OpSL Pß P \GG P MS 13' \:t0) ß( P,'( GP PM \-N GSß SSß NG?ON S Qß 1$' C SP 3\0. DENCO (CLACTON) LIMITED 355-7-9 OLD ROAD, CLACTON -ON -SEA, ESSEX Our components are chosen by Technical Authors and Constructors throughout the World for their performance and reliability, every coil being inspected twice plus a final test and near spot-on alignment as a final check. Our General Catalogue showing full product range DTB4 Transistor & Valve circuitry for D.P. Coils DTB9 Valve Type Coil Pack Application circuity MD 1 Decoder Circuitry for Stereo Reception 28p 28p 28p 28p All post paid, but please enclose S.A.E. with all other requests in the interests of retaining lowest possible prices to actual consumers 651 JUNE 1975 www.americanradiohistory.com When told a pal of mine that the Home Radio Components catalogue costs 65 pence plus 33 pence for postage and packing, he whistled through his teeth and exclaimed "It must be the world's most expensive catalogue!" He changed his tune when showed him my copy and he compared it with the lower priced catalogues he'd already bought. He even finished up by admitting "The dearest is the cheapest in the end". Well, that old saying certainly sums it up as far as catalogues are concerned. With its 240 pages, giving over 6,000 items clearly listed and profusely illustrated, the Home Radio Components catalogue certainly stands out head and shoulders above the rest. And when you remember that the catalogue includes 14 vouchers each worth 5 pence when used as instructed, enabling you to claw back 70 pence of your 98 pence, it's just about the best investment any keen electronics constructor could make. What's more, the catalogue is backed up by a Mail Order I I 65 p. pi s 33 p PPACK N GD Service that takes all the fuss and frustration out of component buying. Why not prove it for yourself ? Send off the coupon below with your cheque or postal order for 98 pence. Then you'll be able to boast to your friends that you own the world's cheapest dearest catalogue! Then, when they ask to borrow it, just let them have a tantalising glimpse but make sure they send for their own - ! Please write your Name and Address in block capitals NAME POST THIS COUPON ADDRESS with cheque or PO. for9'8p. 'The price of 98p applies only to customers in the U.K. and to BFPO addresses. I I HOME RADIO (Components) LTD., Dept. `234-240 London Road, Mitcham, Surrey CR4 RC 3HD Regd. Ma 912966. London HOME RADIO (Components) LTD., Dept. RC, 234-240 London Road, Mitcham, CR4 3HD Phone 01-648 8422 652 RADIO www.americanradiohistory.com & ELECTRONICS CONSTRUCTOR ':aILICÏ A ICS ; CONSTRUCTOR JUNE 1975 Volume 28 No. CONTENTS SUPER -REGENERATIVE 28MHz RECEIVER 11 by Published Monthly (1st of Month) First Published 1947 Incorporating The Radio Amateur F. G. 654 Rayer RECENT PUBLICATIONS 659 NEWS AND COMMENT 660 SEQUENTIAL TRANSISTOR OSCILLATOR 662 (Suggested Circuit 295) by G. A. French Editorial and Advertising Offices 57 MA/DA VALE LONDON W9 1SN Telephone 01-286 6141 Telegrams Databux, London e Data Publications Ltd., 1975. Contents may only be reproduced after obtaining prior permission from the Editor. Short abstracts or references are allowable provided acknowledgement of source is given. Subscription: £4.00 (U.S.A. and Canada S10.00) including postage. Remittances should be made payable to "Data Publications Ltd". Overseas readers please pay by cheque or International Money Order. Annual SOFT AUDIO LIMITER Technical Queries. We regret that we modifications to equipment described. We regret that such queries cannot be answered over the telephone; they must be submitted in writing and accompanied by a stamped addressed envelope for reply. 667 THE BASE TRACER by S. F. May 670 SWITCHING DELAY CIRCUIT by P. F. Hughes INTEGRATED CIRCUIT SUPERHET by R. A. - Part 1 672 Penfold TRADE NEWS 679 THE WHEATSTONE TELEGRAPH by D. P. Newton 680 SOLDERING IRON SAVER 682 by are unable to answer queries other than those arising from articles appearing in this magazine nor can we advise on 665 by A. Foord P. Thomas THE 'SLIDE RULE' RECEIVER CUM CAPACITANCE METER - Part 2 683 by Sir Douglas Hall, K.C.M.G. MAINS FAILURE MONITOR 686 by N. R. Wilson SHORT WAVE NEWS by Frank A. Baldwin - For DX Listeners - 688 Correspondence should be addressed to the Editor, Advertising Manager, Subscription Manager or the Publishers as appropriate. IN YOUR WORKSHOP Operational Amplifiers, 709 Op -Amp 690 RADIO TOPICS by Recorder 696 Opinions expressed by contributors are not necessarily those of the Editor or proprietors. CONSTRUCTOR'S DATA SHEET No. 99 (Resistor Current Values) Production.-Web Offset. Published in Great Britain by the Proprietors and Publishers, Data Publications Ltd, 57 Maida Vale, London, W9 1SN The Radio & Electronics Constructor is Carlisle Web Offset. printed by JULY ISSUE WILL BE PUBLISHED ON 1st JULY www.americanradiohistory.com lil SUPER- REGENERATIVE 28 MHz RECEIVER This article gives details of the construction of a super -regenerative receiver designed for the 28-29.7MHz amateur band. The receiver may be employed in conjunction with the transmitter -receiver described in theMarch-April issues, or with the larger transmitter which will be described later in the series. THIS RECEIVER HAS THE ADVANTAGES THAT IT REQUIRES few components and that no adjustments are needed apart from setting up a single coil core for reception on the 28MHz amateur band. Four transistors are employed and they operate a small loudspeaker at reasonable volume. CIRCUIT OPERATION The circuit of the receiver is given in Fig. 1. TRI appears in an untuned r.f. stage, the main purpose of which is to isolate the aerial and the detector. This reduces aerial radiation and also prevents troublesome hand capacitance effects which could upset tuning. The coil. primary, L1, couples to the tuned winding, L2, and this in turn couples to the drain of the detector, TR2. Feedback from the source to the drain is provided by C5. The regeneration level is controlled by VR1, which is ganged with the on -off switch, SI. The audio section is a 2-stage amplifier comprising TR3 and TR4, and these give a high degree of gain. The collector of TR4 feeds into an 800. speaker. Total battery current is about 20mA and a PP4 battery can be used. If a sufficiently small speaker can be obtained there should be room, alternatively, for the larger PP6 battery. This receiver is very easy to tune and operate. When used with the transmitter to be described in the next two articles in this series, it was found to have sufficient o +9V TRI MPFIO2 SK iD 777 000 G S D MPF102 2N5459 Lead -outs Fig. 1. The circuit BC I09 BC 108 Lead -outs of the super -regenerative receiver. This incorporates two field-effect transistors 654 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com By F. G. Rayer sensitivity for ample speaker volume without the aerial extended at short range, and to provide easy reception with the aerial extended at a range of 5 miles or more across open country. It can be employed for monitoring signals near the transmitter by turning VRI just beyond the point at which Si closes, so that no regeneration is given. So far as components are concerned, it will be noted that VR1 is specified as a 22kû potentiometer. It may alternatively be 20k12 or 25k 12 if either of these values is easier to obtain. The telescopic aerial employed by the author was about 36in. when extended. If an aerial of this length cannot be obtained, nearly similar lengths are given by a type TA3(A) aerial (32in.) or a type TA10 aerial (46in.). Both of these are available from Henry's Radio Ltd. r METALWORK The front panel, top and bottom of the case are made up from a single 8 by 3in. Universal Chassis side, available from Home Radio. V-shaped sections are cut The super-regenerative receiver can be held comfortably in the hand Resistors (All fixed values 1 watt 5%) RI 33052 R2 R3 R4 l kS2 1k52 R5 R6 R7 R8 R9 RIO VR 15kû COMPONENTS Inductors LI, L2 lOkS2 L3 2.2Mû 10kû 56kû 12kû Semiconductors TR1 MPFI02 3952 22k12 potentiometer, linear, with switch SI (see text) Capacitors Cl C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 VCl JUNE detector coil (see text) r.f. choke (see text) 1,000pF disc or tubular ceramic 22pF tubular ceramic 1,000pF disc or tubular ceramic 20µF electrolytic, 10 V. Wkg. 4.7pF tubular ceramic 5,000pF disc or tubular ceramic 0.01µF plastic foil 100µF electrolytic, 10 V. Wkg. 0.1µF plastic foil 2.2µF electrolytic, 10 V. Wkg. 50µF electrolytic, 4 V. Wkg. 10pF variable, type C804 (Jackson Bros.) TR2 TR3 TR4 Switch SI 2N5459 BC109 BC 108 s.p.s.t., part of V R I Speaker 8052 Speaker, 21 in. (see text) Miscellaneous Telescopic aerial, 36 in. extended (see text) 8 x 3 in. Universal Chassis side, (Home Radio) 2 knobs Plain Veroboard, 0. I5 in. matrix, 3 x in. S.R.B.P. and aluminium sheet, as required Nuts, bolts, solder tags, etc. 1975 4 655 www.americanradiohistory.com r m o o o O 0 o 6BA bolt o TR2 o 0 o 0 o CI R3 0 o" o 0 0 O 2 0 C4 o o 1111111111111111111111111010001111101111111110 o R4 a I-. o o o 0 0 0 o o o O 0 0 0 0 o o 0 O 0 0 0 0 0 0 7-r o O O G O o C6 6BA bolts .U. O C7 oC9 0 o 0 4 D 1R50 R1 o 0 R6 o eaClO .--L 0 - Coil Cg -- Battery t - Reo o 2 3 Speaker b c Fig. 2. The component side of the Veroboard panel. Lead 4 of the detector coil shares the same hole as the drain of TR1. TR2, C2 and C5 are mounted on the solder lugs of VC1 from each long flange I$ inch from each end. 1 he ends of the chassis side are then bent through 90° at the V -cut apexes, resulting in an open case having a top, front and bottom with dimensions of 5 by 3 by 1 yin. Naturally, all flanges are on the inside. The sharp bends required are best obtained by gripping the metal between pieces of wood in a vice. What is now the top of the case is drilled to take VR1 and VC1, which are mounted in the positions shown in Fig. 2. The precise positioning of these two components is not important, provided VC1 lugs and spindle will be clear of the Veroboard panel on which the components are mounted. The components are assembled on a piece of 0.15in. matrix plain Veroboard having 19 by 17 holes, and with a section cut out for the speaker magnet, as shown in Fig. 2. It is best to cut out the Veroboard panel at this stage since it enables the speaker positioning to be established. VR1 and VC1 may be temporarily fitted and the required speaker position found with the aid of the Veroboard panel. The author used a small 2kin. speaker and it was found possible to position this and the Veroboard such that ample space was left for a PP6 battery. The Veroboard panel passes over part of the speaker, as may be seen from the photographs of the interior. It is probable that constructors will have to employ a slightly larger 2iin. speaker, but this should still allow room for a PP4 if not a PP6 battery. (Nominal dimensions for a PP4 battery are l in. .diameter by in., whilst those for a PP6 battery are 1,, by â by 2kin.). When the required speaker position has been s le 1 determined, this is marked out on the chassis, and the Veroboard panel and the two controls are removed. Speaker mounting holes and a kin. aperture are then cut out in the front panel at the appropriate points. The back of the aperture is covered with speaker gauze. or similar. Also, the flange on the bottom of the case is cut off to permit easy fitting and removal of the battery. The right side of the receiver (when viewed from the rear) carries the telescopic aerial, and this consists of a piece of s.r.b.p. (`Paxolin') measuring 5 by lain. It is bolted to the side flanges of the case top, front and bottom, and has the aerial secured to it by means òf simple home -constructed clamps. The right side can alternatively be cut from aluminium sheet, whereupon an insulated mounting must be made up for the aerial. The right side is secured permanently to the case. A removable cover can be made up from a piece of aluminium sheet measuring 5 by 42in. before bending. It is bent through 90° along a line 3in. from one 5in. edge, whereupon it covers the back and left side of the case. It is secured to the case flanges with self-tapping 1 screws. 656 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com COIL WINDING The coil, LI, L2, was wound on a hin. diameter former with adjustable core. A suitable alternative former is the Home Radio Cat. No. CR26, with core Cat. No. 7/Z87, this former being 5mm. in diameter and 14mm. long. The winding ends are numbered I to 4 in the diagrams to assist in showing how the coil is wound and connected into circuit. The winding wire is 32 s.w.g. enamelled wire, and one end of this is secured as near the top of the former as possible, using adhesive, cotton or tape. This is .point 1, and 14 turns are then wound side by side, terminating at point 2. A space of approximately ,' in. is left, then 8 turns of the wire are wound on, side by side, in the same direction, starting at point 3 and ending at point 4. Although the winding ends may be fixed with adhesive, the windings themselves must not be covered with adhesive, varnish or any other substances which may cause losses. The r.f. choke, L3, consists of 150 turns of 40 s.w.g. enamelled wire wound side by side on a tin. diameter former without a core. The former could be a length of tin. insulated rod, cut from a potentiometer shaft. The winding occupies about gin., so the former needs to have lin. clear winding space. The ends of the coil are held with touches of adhesive. VC' R2 G L3 Aerial Fig. 3. The wiring on the underside of the board BOARD WIRING The components inside the receiver are laid out in compact manner without crowding J The component and wiring sides of the Veroboard panel are illustrated in Figs. 2 and 3 respectively. Three 6BA clear holes are required for 6BA mounting bolts. These also hold solder tags which provide the chassis connection to the board. The board is spaced about gin. away from the back of the front panel, and the three screws may pass through three holes in the panel, being secured on either side by nuts. However, a neater appearance is given by fitting 6BA threaded spacers, or terminal heads, on the board securing bolts. Three short bolts may then pass into these from the front of the case, so that bolt heads instead of nuts appear at the front panel. Correct matching of the two sets of 6BA clear holes can be assured by placing the board and case front together before wiring, and drilling both at the same time. Coil Ll, L2 is a push fit in a further hole in the Veroboard panel, and is fixed with adhesive. The r.f. choke, L3, can be secured with adhesive at one or both ends. There is no particular cramping of wiring, but care should be taken to ensure that joints and leads around the positive end of C8 will not touch the speaker frame. Tinned copper wire of around 20 s.w.g. runs between the 6BA 'MC' tags, and wires are left projecting to be soldered to VC1 and VR1. Also, thin flexible wires are fitted for connection to the speaker, the aerial and the battery positive terminal. When all the wiring on the board has been completed, it is secured in the case in the manner just described. UNE 1975 657 www.americanradiohistory.com The receiver with its removable cover alongside ADJUSTMENT Connections can then be made to VR I and VCI. Note that TR2, C2 and C5 are not on the board, but are mounted by their connections to VC1. The speaker and aerial are next connected, and battery clips added to the positive battery lead fom the board and the negative battery lead from SI. If bare battery clips are employed these must be taped over to prevent contact with the chassis. If the negative clip touches the metal case the receiver is switched on, whilst if the positive clip touches the metal the battery can be short-circuited. -,,.i .Ti .i siiiïi ..r.z. /1% iiii s iïi:ï:::::: :iï:.::i::i iiii Another view of the completed super -regenerative receiver A signal, either from a signal generator or from a transmitter, is needed for setting up the receiver. VC I is set to half maximum capacitance, and the core of L I , L2 turned until the signal is tuned in. After adjustment, the core can be held in place with wax, or thin elastic run between the core and the former when the core is initially screwed in. The aerial should not be extended when checking near the transmitter, and VR1 should be advanced only a little according to signal strength. For use at a distance, VR1 must be advanced until a hiss is heard, this indicating super -regenerative operation. This hiss ceases when the signal is tuned in, up to the limit of range where signal strength is too low for acceptable reception. The setting of VR1, or the tuning, will not be critical when signal strength is good. When approaching the limit of useful range, or when circumstances are unfavourable, the angle at which the receiver and aerial are held, together with the aerial height, become more important. If desired, a wire or other longer aerial can be attached. When the receiver is in the super-regenerative mode, interference from it can be picked up by another receiver at a small distance. This should not generally be very important on the frequencies concerned, and especially as the receiver is likely to be used away from the house. A super -regenerative detector of this type is usually considered to have a sensitivity of around 1µV, which is greater than that expected from a superhet of average non-specialised type. No particular difficulty is likely to be experienced with the circuit, which is capable of quite long distance reception. If various transistors are tried in the TR2 position it may be found that, with some, the onset of regeneration is more easily controlled than with others. The adjustment of a super -regeneration control is much less critical than the adjustment of a regeneration or reaction control, as used in ordinary t.r.f. receivers, and in fact some commercial equipment employs fixed super -regeneration. However, if any difficulty does arise in this direction, it can be worth -while changing C5 to a low capacitance trimmer of the order of 10pF, this being adjusted for the onset of super-regeneration with VR1 about one quarter from its maximum position. The description of the super -regenerative receiver is now concluded. In the next article in this series, the 30 watt base transmitter will be introduced. RADIO & ELECTRONICS CONSTRUCTOR 658 www.americanradiohistory.com RECENT PUBLICATIONS TOWERS' INTERNATIONAL TRANSISTOR SELECTOR. By B.Sc., C.Eng., M.I.E.R.E. 142 pages, 295 x 210 mm. (114 x 81 in.). Price £2.95. Et Co. Ltd. T. D. Towers, M.B.E., M.A., Published by W. Foulsham This mammoth work gives electrical and mechanical specifications for over 10,000 American, British, European and Japanese transistors. The transistors appear in numero -alphabetic order and each is accorded a single line in the tables which constitute the bulk of the book. Entries are given in the following columns: polarity and material (i.e. germanium or silicon), case outline, lead identification, VCBO max., VCEO max., VEBO max., IC max., Tj max., Ptot. max., FT min., COB max., HFE, HFE bias (i.e. current at which HFE is quoted), use, manufacturer, suggested U.K. substitute and suggested U.S.A. substitute. There are 80 transistor types per page, and to give an idea of range the 2N series starts at 2N22 and ends at 2N6368 some 41 pages later. Again, the Japanese 2SA to 2SD range occupies more than 23 pages. This is a most valuable reference source for anyone who has to find his way through the fantastically large number of transistors which are available these days, and it provides a welcome short-cut to the essential data on any of the very large number of devices that it lists. ELSEVIER'S DICTIONARY OF TELEVISION AND VIDEO RECORDING. Compiled by E. Clason. 616 pages, 220 x 150 mm. (84 x 6 in.). Published by Elsevier Scientific Publishing Company. Price: see below. This book gives English/American, French, Spanish, Italian, Dutch and German translations of technical terms employed in modern television and video recording work. The basic language is English, and 420 -odd pages of the dictionary give translations in the other five languages of 5,310 English terms listed in alphabetical order. In many instances an English definition of the term is given before the translations. Each term is numbered. If the reader wishes to find the English translation for a French term he consults the French section of the dictionary, which lists all the French terms with their translation numbers in the main English section. This procedure also leads to the corresponding translations in the other languages. Following the French section are Spanish, Italian, Dutch and German sections which similarly allow the reader to find the English translation W. number. The work is based on Elsevier's Dictionary of Television, Radar and Antennas, which has been completely revised and brought up to date. The dictionary is extremely comprehensive and detailed, and will be of great help to the engineer who consults technical texts in the languages covered. The book is published in the Netherlands by Elsevier Scientific Publishing Company, P.O. Box 211, Amsterdam, and the review literature quoted the price as Dfl 135.00 or about 51.95 U.S. dollars. BEGINNER'S GUIDE TO TRANSISTORS, Second Edition. By J. A. Reddihough and I. R. Sinclair, B.Sc., C.Eng., M.I.E.E., M.Inst.P. 162 pages, 185 x 125 mm. (74 x 5 in.). Published by Newnes-Butterworths. Price £1.80. The first edition of this book was written by J. A. Reddihough and appeared in 1968. It has now been completely revised for the second edition by I. R. Sinclair. The book commences with a simple description of how a transistor works, then carries on to related semiconductor devices such as f.e.t.'s, unijunction transistors, junction, point -contact and zener diodes, tunnel diodes and thyristors. Next discussed are amplifier configurations, parameters and basic amplifier circuits. Succeeding chapters deal with a.f. circuits and techniques, including tape recorder circuits and differential amplifiers; r.f. circuits and techniques, at frequencies up to u.h.f.; the transistor employed as a switch; power supplies and integrated circuits. A final chapter gives hints on fault finding and servicing. The book gives clear explanations which are backed up by well presented diagrams, and will be found particularly useful to the beginner who is embarking on work with semiconductors either as a hobby or as a career. J 659 UNE 1975 www.americanradiohistory.com NEWS . AUDIO PICTURES AND RADIO CONTROL SYSTEM SOVEREIGN SERIES Talking pictures, audio sculptures, radio paintings they're all the same to Kit Penny, a former art student who is creating the latest top executive `toy' in a studio at the back of his father's pub, The Balls Hut Inn, Fontwell, near Arundel in Sussex. In one of his flurries of creative activity, Kit knocked a transistor set over - the cabinet broke into a dozen pieces and the-instrument remained mute. The only flat working surface was the canvas on which Kit was working and this was removed from the easel and placed on the floor. Later, the entrails of the radio were spread over a canvas that measured about . - Flight Link Control Ltd., of Bristow Road, Hounslow, Middlesex, who specialise in designing and manufacturing professional -standard radio control equipment for industrial as well as consumer markets, have standardised on Portescap's type 032 DC micromotor for the servo system in their latest radio -control system - the Sovereign Series. This is the motor that they have been using successfully for more than six years in their radio -control products. The result has been that the company can now offer what they believe to be the highest quality range of 2, 3, 4, 5 or 6 -function radio -control units ever made available on the British market. The servo, which is used to provide the remote mechanical movements that are hand controlled at the transmitter unit, is a tiny (1.6 x 1.35 x 0.95 in.) lightweight (2 oz.) device. It incorporates a motorised potentiometer, which is driven by a type 032 motor having a built-in 15:1 reduction gearhead. These micromotors are precision engineered units having patented ironless skew -wound rotors that ensure a high power-to -weight ratio and low current consumption. They also incorporate precious metals in the commutator (silver alloy) and brushes (gold alloy) and feature self-lubricating sintered bronze bearings, all of which features contribute to their long life, high reliability and maintenance -free operation. Such features are essential in any servo system, particularly in the case of Flight Link Control's airborne equipment. Using the type 032 - they purchase large numbers every year - they can offer servomechanisms that produce a pull of 3.25 lb. over i-inch travel and are claimed to provide the smoothest, quickest and most precise control response available anywhere at a comparable price. 30 x 20 in. Considering what he now believed to be a pile of worthless junk, Kit was struck by the attractiveness of of the design the radio components made against the background of canvas. Two weeks later, and having used considerable quantities of impact adhesive (the canvas had been exchanged for fibreboard) and three tins of aerosol paint, Kit was considering his first talking picture ... or audio sculpture if you like. A loose wire soldered to its proper connection and the first talking picture, the prototype of many more, talked. Kit has produced a number now, they sell at about £45.00, and each design is exclusive: the idea has been patented. Details from Talking Picture Company, Fontwell, Arundel, Sussex. 660 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com COMMENT RADIOMOBILE CONSOLES assembly is simply fitted into the car and has no visible screws or brackets, resulting in a smart centre console styled in black moulded, padded plastic on strong hardboard which is used in preference to wood which would split in case of an accident. Radiomobile Consoles are provided with a loud speaker grill, a radio heat shield to prevent over-heating from the car's heating system and all the necessary screw fixings etc., with easy to follow installation instructions. One of the features of the new Console, is that the cut-out has been strengthened to accommodate stereos, and vastly improves the dash -board without impairing safety standards. The Consoles are available only from Radiomobile dealers price £10.45 excluding VAT. Radiomobile Limited have made life easier with a selection of new attractively -styled radio Consoles. The radio and speaker can be mounted into the Console outside the car, prior to installation. The whole SINCLAIR RADIONICS WINS QUEEN'S AWARD It gave us particular pleasure to learn of the above award as Clive Sinclair, prior to founding Sinclair Radionics Ltd., of London Road, St. Ives, Cambs., was an occasional contributor to these pages. The company has won a Queen's Award to Industry, 1975 in recognition of its outstanding export achievement and for technological innovation in scientific electronic calculators. It is Europe's largest manufac- turer of electronic calculators. Award for technological innovation has been made for the development of the low cost, Sinclair `Scientific' pocket calculator which replaces slide rules and four figure tables. Clive Sinclair not only founded the company, but is also its Managing Director. CASH NEEDED FOR AMSAT-OSCAR 8 PROJECT AMSAT is trying to raise $15,000 needed for the development of advanced hardware for the AMSAT-OSCAR 8 project. Currently under development are 146 -to -435 -MHz repeaters, new telecommand and telemetry systems, and on -board microprocessor controlled systems for applications in future AMSAT-OSCAR spacecraft. Donations can be sent to Radio Amateur Satellite Corporation, P.O. Box 27, Washington, D.C. 20044. In co-operation with AMSAT, Skip Reymann, W6PAJ has published an AMSAT-OSCAR orbital data calendar containing all orbits for 1975 for both AMSAT-OSCAR 6 and AMSAT-OSCAR 7. The orbital data calendar is available postpaid for 20 IRC's. Overseas orders will be shipped via airmail. Orders and payment should be made to: Skip Reymann, W6PAJ, P.O. Box 374, San Dimas, California 91773, U.S.A. All excess receipts over costs will be donated to AMSAT. A Stand devoted to O.S.C.A.R. was a feature of the Exhibition staged recently by the Norwich Astronomical Society. Much interest was shown in it as it demonstrated the `overlap' of the sciences these days, in this case that between radio and space activities and the more traditional aspects of astronomy. "So all these anti -static precautions of yours are strictly down to Advanced Technology eh l Mr. Poskitt ?" 661 1UNE 1975 www.americanradiohistory.com SEQUENTIAL TRANSISTOR OSCILLATOR By G. A. French INTHE `SUGGESTED CIRCUIT' ARTICLE which appeared in last month's issue the writer described a sequential switching circuit by means of which a `moving light' impression could be' achieved in a rectangle of lamps. Successive lamps were extinguished in turn, the whole system being controlled by an oscillator comprising three transistors. The oscillator design is, on its own, of sufficient interest to merit further attention in a second article, and aspects concerning its operation which did not need to be referred to in last month's switching lamp application will now be dealt with. Suggested Circuit 295 The oscillator is self-starting, and it three transistors to be germanium types as silicon transistors do not have reverse base emitter voltage ratings which are high enough for the present application. Also, the voltages on the bases and emitters of conducting silicon transistors would cause reverse polarising voltages to be applied to the electrolytic coupling capacitors. An important feature of the oscillator is that at least one transistor in the ring must always be fully turned on to break any linear is necessary for the amplification chain. through the three, as feedback would otherwise become degenerative and the oscillator would cease to function. The oscillator will, in consequence, only run at relatively low frequencies. In last month's atticle the oscillator was made to run at about 12Hz, which is approaching the limiting highest frequency at which it can function. At this frequency, the three coupling capacitors were 4µF electrolytic, and it was necessary for these to have low leakage currents for oscillator operation to take place. -9V OSCILLATOR CIRCUIT The oscillator circuit is shown in Fig. 1 and it comprises three transistors, two of which are always on and one of which is always off. Oscillator functioning was fully described in the previous article and so only brief details will be given here. When, during the cycle, TRI turns off, capacitor Cl is able to charge to nearly the full supply voltage by way of R2 and the base -emitter junction of TR2. Later, TRI turns on again whereupon the charged Cl takes TR2 base positive of the lower supply rail and turns off this transistor. C2 charges, in turn, via R4 and the base -emitter junction of TR3, whilst CI discharges at a lower rate into R3. When Cl has discharged sufficiently TR2 turns on, whereupon the charged C2 causes TR3 to turn off. The cycle continues around the ring of transistors in this manner, with the transistors turning off successively in the order: TRI, TR2, TR3, TRI, TR2, TR3. External circuits may be controlled by switching transistors inserted in the collector circuits of the oscillator transistors. RI IOkn Ikn TRI ACY 19 R1 -R6 1/4 CI -C3 see c watt 10% text AC Y 19 Lead -outs Fig. 1. The basic three transistor sequential oscillator. The transistors turn off in sequence 662 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com When the three coupling capacitors have values of 10µF or more the requirements for low leakage current are not so stringent and the oscillator runs with capacitors having leakage currents that fall within manufacturers' specifications. Even so, it is desirable to employ reasonably new capacitors of modern design and not capacitors which have seen extended periods of service in other equipment or which have been knocking around in a junk box for â long time. With coupling capacitors of 100 to 200µF the oscillator completes a cycle in a period of several seconds and it then becomes attractive for applications in which sequential control of three functions is required. The main advantage of the oscillator is the fact that it is so simple; only three transistors, three capacitors and six resistors are required. CAPACITOR VALUES Up to now, references to the oscillator have assumed that all three coupling capacitors have the same nominal capacitance. This is the preferred method of operation because there is a slight lag between the turnoff of an oscillator transistor and the consequent cutting off of a switching transistor in its collector circuit due to the charging of the capacitor coupling to the following base, and an excessively large capacitance in one position would result, in a disproportionately high time lag. It should be remembered also that one capacitor in the oscillator has to become charged well before the capacitor preceding it is discharged. Because of these factors it is better to run the oscillator with all three capacitors having the same nominal value. Oscillator frequency varies inversely with capacitor value. When the three capacitors have a value of 100µF the length of a complete cycle is a little longer than 2 seconds, with 200µF it is about 4.5 seconds, and so on up to about 11 seconds with 500µF. Oscillator running is a little erratic when the coupling capacitors have values much above 1,000µF, and so it would appear reasonable to state that the maximum capacitance for reliable operation is 500µF. At lower capacitances oscillator frequency is increased, being one cycle in about 0.2 sec., or 5Hz, with 10µF, and at intermediate values for capacitances up to 100µF. Below 10µF, capacitance leakage current becomes more important and a minimum capacitance value for reliable operation would be of the order of But, instead of one turned -off transistor it was found that there were two turned -off transistors running round the ring! TRI and TR3 both turned off and on at approximately the same times, as did TR2 and TR4. Much the same occurred with the five transistor circuit of Fig. 2(b). Again, there were two turned-off transistors running round the ring although this time the turning on and turning off of any two transistors did not coincide. The circuits of Figs. 2(a) and (b) are amusing and instructive, but, regrettably, do not offer any obvious practical application. ages and there is a very slight risk of small reverse voltages appearing in the circuit. The author has checked circuit operation with ACY19 transistors. Other transistors in the same immediate `family', i.e. ACY17 to ACY21, will probably function equally well, but these have not been tried by the author. The oscillator runs at supply voltages lower than 9 volts, with 4.5 volts representing a minimum satisfactory figure. FURTHER STAGES As shown in Fig. 1 the oscillator has, effectively, a turned -off transistor running continually around the ring of three transistors. It was decided to add one or more stages to see if the same effect could be achieved -with a larger number of transistors. The four transistor circuit of Fig. 2 (a) was first checked. This also oscillated reliably and was self-starting. EXTERNAL SWITCHING It will be desirable for the three transistor oscillator to control external circuits, and this can be achieved by inserting switching transistors in the collector resistor circuits. For external loads up to 100mA a single BC 107 may 9V RI IOkn IOkn IOkn ^4 2 Ikn 6 Ikn CI R7 IOknR8 R5 R3 Ikn Ikn C C4 + IOOpF 1OOpF IOOpF IOOpF TRI TR2 TR3 TR4 ACYI9 ACV 19 ACYI9 ACY 19 (a ) -9V IOkn Ikn Ikn R8 R6 R4 C1 IOkn IOkn IOkn IOkn R2 R9 R7 R5 R3 RI c2 I kn C3 I kn + 1+ IOOpF IOOpF R10 c4 Ikn arIOOpF IOOpF IOOpF TRI TR2 TR3 TR4 ACYI9 ACYI9 ACYI9 ACYI9 C5 TR5 ACYI9 2µF. All these capacitance values refer to aluminium electrolytic capacitors with their normal wide tolerance on value and having working voltages of 10 volts or more. The author has not tried tantalum capacitors in the oscillator. Some tantalum capacitors can be damaged by reverse polarising volt - (b) Fig. 2. (a). An experimental oscillator employing four transistors (b). Here, five transistors are coupled in sequence . UNE 663 1975 www.americanradiohistory.com -9V BUY THIS 2-2kn 1/4 watt BC107 hingaistor BEST SELLER etSrwintcs R2 R4 or R6 Ikn NEW EDITION OF External load TRI TR2 T.V. FAULT FINDING External load or TR3 405/625 LINES b w C BC107 AC 187 Lead-outs Lead -outs (a) (b) -9V 2 2kn 1/4 watt 2N3055 100/0 R2 R4 REVISED & Fig. 3 (a). A switching tran- ENLARGED Edited by J. R. Davies 132 pages Price 90p Over 100 illustrations, including 60 photographs of a television screen after the appropriate faults have been deliberately introduced. sistor circuit for low external load currents (b). A small power transistor is employed for larger currents in the external load (c). This circuit can switch load currents up to several amps or R6 External load TR1 TR2 or TR3 e Comprehensive Fault Finding Guide to cross-referenced methods of fault rectification described at greater length in the text. 2N3055 Lead -outs (C) Price 90p from your Bookseller or post this Coupon together with remittance for £1.02 (to include postage) to DATA PUBLICATIONS LTD. 57 Maida Vale, London, W91 SN 1 Please send me the 5th revised edition of TV Fault Finding, Data Book No. 5 I enclose cheque / crossed postal order for NAME ADDRESS L Block Letters Please be inserted, as in Fig. 3(a). If the external load is between 100 and 500mA, the switching transistor may be an AC187, as indicated in Fig. 3(b). For loads up to some 4 amps, the arrangement shown in Fig. 3(c), in which an AC187 is used in conjunction with a 2N3055 should be employed. A check on switching transistor temperature should be initially carried out with the circuits of Figs. 3(b) and (c), and a heat sink should be fitted to any transistor which shows evidence of running warm. If the switching transistors remain cool, as will probably be the case, no heat sink is required. The switched load circuits are shown as being returned to a separate positive rail, this being decoupled from the oscillator positive rail. Such an ap- 664 proach is desirable if load currents are high, since it ensures that switching surges do not affect the oscillator. For load current of around 100mA or less, the load and oscillator circuits could share the same negative and positive rails, provided these are adequately bypassed by a high value capacitor. It was mentioned earlier that there is a slight time lag between the turning off of an oscillator transistor and the cutting off of the switching transistor in its collector circuit. The time lag will normally be too short to be significant, but it can be reduced if desired by employing a lower value resistor in. place of the 2.2k52 component shown in Figs. 3(a), (b) and (c). With a 9 volt oscillator supply, values down to 13052 may be substituted. RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com SOFT AUDIO LIMITER Our contributor discusses two low level voltage limiting circuits, one of which gives hard limiting whilst the other provides soft limiting. By A. Foord AN AUDIO AMPLIFIER WHEN IS ALLOWED TO CLIP without control some listener irritation is bound to occur, for two reasons. Firstly, because the limiting action is usually hard and a profusion of harmonics are generated. Secondly, because the negative feedback characteristics of the amplifier alter and spurious high frequency oscillations may occur for the duration of the overload. If soft limiting is applied to an audio power amplifier there are several benefits. Soft limiting is defined here as a linear amplification up to at least half of full amplitude with progressive compression of larger amplitudes. Recovery from the ever-present peak inputs would be very rapid. The input voltage that would cause complete saturation would be increased, giving the illusion of a Pre -amp section greater power reserve. High quality need not be sacrificed since the amplifier output can be linear to within 3dB of its maximum output. Suitable compression networks using diodes or zener diodes are simple and can be added around an existing power amplifier or between the pre -amplifier and power amplifier. BRIDGE HARD LIMITING CIRCUIT Initial experiments were conducted with the circuit of Fig. 1. Here, ICI represents the last stage in the preamplifier. A low output impedance is required because of the low value of RL which has to be driven. If the output of the preceding stage has a zero voltage d.c. Limiting section 0 56V 000 c b e TRI O.I}iF 2N4126 2 N4124 2N4126 Lead -outs Input 0.47íF 2.7kn ICI SN72741 L or I 7 C~11 IN914 Output limiting level ±2V ir D3 * + D2 27kn 8 7 27kn B-2kn IN914 6 IN914 D4 t +IN914 10}1F 12 RL 22On f.-.--0Output Ikn lin. o OV 4 3 +I5V 470n SN72741P 27kn Top view 1 8 TR2 2N4124 7 1 0 0 2 0 0 56V 6 47On 3 4 o -15V SN72741L Top view Fig. JUNE 1. A circuit which gives hard limiting 1975 665 www.americanradiohistory.com SOFT LIMITING CIRCUIT For high quality applications an alternative arrangement must be used, and a suitable circuit is shown in Fig. 3. Here a slightly different form of diode bridge is placed in the negative feedback path of an integrated circuit, ICI. Under small signal conditions D1 and D2 are forward biased (by R3 and R4) and D3 and D4 are reverse biased. Then the overall gain is unity, as determined by R1 and R2. However, for large positive -going signals D2 and D4 become forward biased. Similarly for large negative going signals D1 and D3 become forward biased. This increases the negative feedback for large signals and reduces the gain. The limiting effect on a sine wave is shown in Fig. 4. Fig. 2. The limiting effect on a sine wave given by the circuit of Fig. 1 3 of the i.c. can be used; otherwise the input coupling can be capacitive, as shown. Transistors TRI and TR2 generate and sink a constant current of IOmA. This divides equally into I1 and I2 which forward bias the diodes D1, D2, D3 and D4. Since the diode bridge is symmetriçal, both the input and output of the diode bridge will be approximately at earth potential under no -signal conditions. For small signals the diodes remain forward biased and the gain of the diode bridge is 0.94 times. However for large signals the maximum possible output level is determined by the constant current and the load resistance RL. Thus the output limiting level is approximately plus or minus 2 volts. The limiting effect on a sine wave is shown in Fig. 2. This is a hard limiting circuit and non-linearities in the diode bridge produce a distortion level of up to 2% for all output levels up to 1 volt r.m.s. Such a simple circuit, with the network betweén the pre-amplifier and power amplifier, can only be justified where the 2% distortion is acceptable. Possible examples include public address and electronic music applications. level then direct coupling to pin o +I5V R3 IBkn Output limiting level ±13V RI 2 --1--'vVh---- Input C2 10kn IOp 6 C41 r is PERFORMANCE Since the diodes are within the feedback loop the distortion is kept low until limiting starts. The total harmonic distortion is less than 0.1% up to an output level of 0.7 volt r.m.s. (1.98 volts peak -to -peak). This rapidly increases to 1.1% at 0.8 volt r.m.s. (2.26 volts peak -to -peak). The nominal limiting level is 0.919 volt r.m.s. (2.6 volts peak -to -peak). Thus the circuit generates very little distortion up to 75% of the limiting level. To set up the circuit, the output potentiometer VRI should be adjusted so that the power amplifier cannot be overdriven no matter what the setting of the preamplifier gain control. COMPONENTS ICI SN72741L or P a sine wave F Cl IOpF Fig. 4. The soft limiting effect on shown here R4 IBkn VR I0kn lin. o oV O.IpFT -15V o Fig. 3. The preferred soft limiting circuit In both the circuits, the i.c. can be SN72741P (8 pin d.i.l.) or SN72741L (8 pin round can). The pin numbers connecting into circuit are the same for both versions. No connections are made to pins which do not appear in the circuits. The fixed resistors are all â watt 5%. In Fig. 3 capacitors C1 and C2 can be electrolytic, and their polarities will depend on the d.c. levels of the preceding and succeeding stages. If d.c. levels here are at earth potential they may not be required. C3 and C4 are ceramic. 666 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com The BASE TRACER By S. F. May This inexpensive switching circuit determines the base lead -out and the polarity of any unknown bipolar transistor. HOME CONSTRUCTORS, EXPERIMENTERS AND SERVICE engineers do not need to be reminded of the vast number of bipolar transistors in existence these days which have unfamiliar or defaced type numbers or which are even completely unmarked. Problems arising from these transistors consist primarily of determining whether they are n.p.n. or p.n.p. and of finding the lead -outs which correspond to base, emitter and collector. The fact that an unknown transistor is in a familiar encapsulation is not always of assistance here, since it is quite common for transistors with the same encapsulation to have quite different lead -out layouts. A very advanced design for the determining of transistor polarity and lead -outs is the `Transistor Lead Locater' described by J. R. Davies in the October and November, 1974, issues of this journal. By means of two rotary switches and a display of four l.e.d's this instrument is capable of finding both the polarity and the individual lead -outs of any normal bipolar transistor, and it has the advantage of high speed of operation. BASE TRACER 3 BY' Test terminals am 3V 3 S2 R1 A TIL209 Lead -outs IBOn I/4w 10% rr A LEDI C TIL209 1. The circuit of the base tracer unit. The only components required are two switches, an l.e.d., a resistor and a battery Fig. The switching circuit to be described in the present article does not pretend to have a performance approaching that of the previous design, and it requires two separate operations to ascertain lead -out layout. On the other hand it is extremely inexpensive and easy to assemble. Two 3 -way switches and an 1.e.d. are employed, and they determine the polarity and the base lead -out of the unknown transistor. The collector and emitter are then found by checking the transistor on a normal transistor gain meter or by using a second test circuit which is described later in this article. The circuit of the device is shown in Fig. 1, in which the two switches are designated S1 and S2. The switch contacts and the three test terminals are numbered 1, 2 and 3. and it will be obvious that the l.e.d. will light up when both switches are set to the same number. The series resistor, R1, limits the l.e.d. current to some 5 to 7mA, and the supply voltage is 3 volts only. These low values of current and voltage are unlikely to damage any transistor being checked. JUNE SI The leads of the unknown transistor are connected in any manner to the three test terminals. S2 is then set to position 1 and SI is taken through its three positions. The l.e.d. is bound to light at one setting of SI and may light at a second setting. If it lights at all three settings of S1 then the test is complete and the transistor polarity and base lead -out have been found. Should the l.e.d. light at only one or two settings of SI, S2 is set to position 2 and SI is taken through its three settings once more. Should this not yield a light at all three settings, S2 is set to position 3 and SI is once more taken through its three positions. If it has not been possible yet to obtain illumination of the l.e.d. for all settings of Si, this switch is set to position 1 and S2 is taken through all its settings. Should the l.e.d. light at all three settings then the test is at an end. If,not. S1 is set to position 2 and S2 taken 667 1975 www.americanradiohistory.com Test Test transistor transistor/ (a) (b) Fig. 2 (a). Typical circuit conditions when an p.n.p. transistor is connected to the test terminals (b). The circuit given when an n.p.n. transistor is connected through all its positions. If this still yields no success, S1 is moved to position 3 whereupon, unless the transistor is open -circuit, the l.e.d. should finally light up at all settings of S2. As can be imagined, the procedure of taking SI and S2 through their settings takes much longer to describe than it does to carry out. What is aimed at is a switching pattern which causes the 1.e.d. to be illuminated at all settings of either SI or S2. If the l.e.d. lights up at all settings of Si then the unknown transistor is a p.n.p. device and the arm of S2 is connected to its base. Should the l.e.d. be illuminated at all settings of S2 then the unknown transistor is an n.p.n. type and Si arm is connected to its base. TRANSISTO,R JUNCTIONS The reason for this beheaviour of the switching circuit can be readily understood if the circuit is redrawn with a transistor connected to the test terminals. This is done in Fig. 2(a), in which the transistor is a p.n.p. type with its emitter connected to terminal 1, its base to terminal 2 and its collector to terminal 3. S2 is in position 2, thereby connecting to the transistor base. Putting Si to position 1 allows current to flow from the positive rail through the forward biased emitter -base junction of the transistor to S2 and thence to the l.e.d., which lights up. Setting S1 to position 2 allows current to flow to the l.e.d. via the direct connection between the two switch contacts. When S1 is set to position 3, current flows through the forward biased collector -base junction of the transistor to S2 and the l.e.d., which once more lights up. It is only possible for the l.e.d. to light up at all three settings of Si when S2 connects to the transistor base. There is no other switching combination which allows either Si or S2 to illuminate the l.e.d. at all three settings. If the p.n.p. transistor had had its base connected to terminal 1, S2 would have needed to be switched to position 1 to obtain a light at all settings of S l Similarly, S2 would have had to be in p3sition 3 if the transistor base had been connected to terminal 3. Fig. 2(b) shows the situation when an n.p.n. transistor is connected to the test terminals. Again, for ease of presentation, the emitter is connected to terminal 1, the base to terminal 2 and the collector to terminal 3. When S1 connects to the base at position 2, the circuit to the l.e.d. is completed via the base -emitter junction with S2 in position 1, via the direct connection with S2 in position 2 and via the collector -base junction with S2 set to position 3. Again, there is no other switching pattern which allows the l.e.d. to light up at all settings of Si or S2, and the arm of Si connects to the transistor . base. There is no need to provide an on-off switch for the unit. When out of use, the two switches are set to different numbers to break the circuit to the l.e.d. PRACTICAL VERSION The circuit may be assembled in a small case having the front panel layout shown in Fig. 3. The two switches are fitted with pointer knobs and the front panel is covered with white card or a similar material on which are drawn three lines joining the test terminals to the three corresponding positions taken up by the switch knobs. The test terminals and switch contacts have the same general layout as in Fig. 1. As shown in Fig. 3, the arms of both switches connect, via their contacts, to the left-hand test terminal There is no need to use the numbers 1, 2 and 3 on the front panel card. Since it is difficult to remember the switching relationships, a legend summarising the situation is written alongside each switch. 668 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com LEDI LIGHT ALL POSITIONS: P.N.P. TRANSISTOR, S2 POINTS TO BASE Pointer Test knobs terminals LIGHT ALL POSITIONS S2 N.P.N. TRANSISTOR, SI POINTS TO BASE Fig. 3. A suitable front panel layout. All legends and lines inside the rectangle are written or drawn on the panel mentioned, this process may be carried out with the aid of a standard transistor gain meter. Alternatively, the circuit shown in Fig. 4 can be used. In Fig. 4 there are two separate sections for p.n.p. and n.p.n. transistors because it is simpler to provide two separate circuits here than to use a single set of components with polarity switching. If an n.p.n. transistor is to be checked it is connected to the n.p.n. test terminals. It will then function as a common emitter amplifier if the emitter connects to the negative rail, whereupon the base current flowing through VRI and R2 will produce a collector current sufficiently high to illuminate the l.e.d. in its collector circuit. Unfortunately, the symmetric construction of a junction transistor allows it to function as an amplifier with the emitter and collector transposed, but the current gain then given is less than that produced when it is connected correctly. It is for this reason that the variable resistor, VR1, is included in the base circuit. The transistor should be connected up with VR1 set to insert minimum resistance. If the I.e.d. lights up, VR1 is adjusted until the l.e.d. is just illuminated, after +3V The unit functions satisfactorily with all germanium and silicon bipolar transistors, but a little care is needed when checking germanium power transistors. This is because some germanium power transistors exhibit relatively high leakage currents, and these may be sufficient to illuminate the 1.e.d. at reduced level when they flow through a reverse biased junction. In consequence the situation may arise in which either SI or S2 causes the l.e.d. to be fully illuminated at two settings and to be partly illuminated at the third setting. Such indications should be ignored and the final switching pattern should be found which causes full illumination at all three switch settings. P.N.P. terminals VRI Base R4 Base EMITTER AND COLLECTOR P.N.P. test o LED2 VR2 II After the base lead -out and the polarity of the unknown transistor have been found it is necessary to determine the emitter and collector leads. As already test / LED3 test terminals N.P.N. Fig. 5. The addition of a commutating switch at each set of test terminals considerably speeds the process of finding the emitter and collector leads terminals +3V VR1 fj . 25Okn lin. N.P.N. test terminals R2 -R5 1/4 watt 10% Fig. 4. A circuit which enables the emitter and collector of the test transistor to be determined JUNE which the collector and emitter leads are changed over. The connection which allows 1.e.d. illumination with the higher value in VR1 is the correct one, and with this the transistor emitter is connected to the negative rail and the collector to the 1.e.d. circuit. If a very high gain transistor is connected up in the correct manner the l.e.d. may still be lit when VR1 inserts maximum resistance, but it should still be possible to differentiate between the correct and incorrect forms of connection. A p.n.p. transistor is checked in the same way, except that it is connected to the'p.n.p. test terminals and it is VR2 which is adjusted. The process of determining the emitter and collector can be greatly speeded by adding a commutating switch at each of the two sets of test terminals, as in Fig. 5. The switch is simply flicked from one position to the other as VR1, or VR2, is adjusted, and the difference in l.e.d. illumination can then be assessed instantaneously. The switches can be mounted on a front panel which is also covered with a white card. This can carry legends alongside each switch which indicates the circuit they set up. 1975 669 www.americanradiohistory.com SWITCHING DELAY CIRCUIT By P. F. Hughes An inexpensive delay circuit which functions without thermal devices or high value electrolytic capacitors. AUTOMATIC DELAY CIRCUITS WHICH PREVENT THE application of power for a period are encountered occasionally in electronics, and a particular instance is given with higher power amateur transmitters incorporating valves. Here, it is desirable to delay the application of h.t. voltage, after switch-on, until the lower voltage circuits have warmed up. A common approach with transmitters consists of employing devices incorporating bimetal strips to delay the switching on c f h.t., but these do not always reset immediately after completing a delay cycle. Circuits using a charging capacitor can also be used, but if a long delay, of the order of 1 minute, is required the capacitor has to be a large value electrolytic component with its attendant leakage current problems. The delay circuit to be described here can offer delay periods of up to several minutes. It employs a capacitor to provide the delay, but this needs a relatively low value only and can be a plastic foil, rather than an electrolytic, component. The only other parts needed in the delay circuit proper are two resistors, two small silicon transistors and an on -off switch. A third transistor, functioning as an emitter follower, couples the delay circuit to a relay coil. CIRCUIT FUNCTIONING C1 - see text R1,R2-1 /4 watt 10% BC107 Lead -outs switching delay circuit. The value of Cl, which is a plastic foil capacitor, is effectively multiplied by the voltage gain of TR1 and TR2 The The circuit appears in the accompanying diagram. When SI is in the 'Off' position the positive rail couples to the base of TRI via RI. The consequent base If S1 is now moved to 'On' supply is current causes both TR1 and TR2 to turn on, and the disconnected from Rl, whereuponthenopositive voltage at TR2 collector is close to the negative supply is available from the supply for TRI. base bias current line. In consequence, the voltage on TR3 emitter is bias current is still available from However, a base equal to or only slightly above that on the negative whose left-hand terminal is positive ofthethecharged Cl, collector of line and the relay does not energise. The current drawn TR2. The bias current required from the 12 volt supply under these circumstances is and the overall effect is that Cl by TRI is very low discharges gradually. about 1.2mA via R1 and R2. At the same time, Cl As it discharges, the collector of TR2 goes slowly is charged to a voltage which is very nearly equal to the positive, keeping up a balance in which the sum of the supply voltage. voltage at TR2 collector and that across the capacitor is 670 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com always just sufficient to provide the bias current needed The value required in Cl depends upon the voltage to maintain the collector current. of TRI and TR2 and the coil voltage at which the The low rate of rise in TR2 collector voltage may gain relay energises. In consequence, Cl has to be deterperhaps be more readily understood when it is appreci- mined experimentally. This is not a difficult task because ated that CI is returned to the inverting input at TR1 length of the delay varies in approximately linear base; the effective value of the capacitor is then multi- the manner with capacitance value; it is only necessary to plied by the total voltage gain of TR1 and TR2. carry out a trial run with a known capacitance and then calculate the value needed for the actual delay required. RELAY COIL CURRENT The author initially checked the circuit with a 1µF capacitor in the Cl position and found that the delay The voltage at TR2 collector is passed by way of the was 68 seconds. a 0.1µF capacitor the delay was emitter follower, TR3, to the relay coil. When it is approximately 7 With seconds, with a sufficiently high the relay energises and its contacts (not approximately 35 seconds, and 0.5µF capacitor it was so on. To see what shown in the diagram) switch on the delayed circuit. effect different transistors gave, the BC107's in the TRI The delay is now over and all that happens subsequently and TR2 positions, were removed and two others is that the voltage at TR2 collector continues to rise up in their place. This time the 1µF capacitor until, eventually, it is close to the voltage on the connected gave a delay of 85 seconds, with proportionate times positive supply line. with other capacitance values. If at any time during or after the delay period S1 is set given It is recommended that the circuit be initially run to 'Off', the circuit reverts to its initial state with the with 1µF capacitor in the Cl position and the length relay de -energised and capacitor Cl charged. Another of thea delay noted. The required alternative value can delay period will then be given if SI is once more set then be calculated and wired in. to 'On'. As a final point, DI is the usual reverse biased diode The relay is not at all critical and the only main connected across the relay coil to prevent the requirement is that it should have a coil resistance of of a high back e.m.f. voltage when the relay de formation -energises. 250û or more, and that it should be capable of energis- This diode must be wired into circuit correct way ing reliably at around 9 volts or so. The prototype round as, otherwise, excessive current will flow in it circuit employed a P.O. 3000 relay with a 50052 coil. and in TR3, with the risk of consequent damage. IN NEXT MONTH'S ATTRACTIVE ISSUE THREE BAND SHORT WAVE PRESELECTOR Covering 1.65 to 32.5MHz in three switched bands, this preselector provides an extra tuned amplfier stage for insertion between the aerial and a short wave receiver. 500mW WORKSHOP ANNUAL INDEX AMPLIFIER August 1974 to July 1975 PLUS MANY OTHER ARTICLES ON SALE 1st JULY RADIOu 1 ;II 1 CONSTRUCTOR JUNE 1975 PRICE 30p Copies may also be obtained direct from the Publishers, 38p including postage. Published by Data Publications Ltd., 57 Maida Vale, London W9 1SN. 671 www.americanradiohistory.com i N TEGRATED CII P By R. A Covering the star band together w bands from 180i superhet receives, the R.C.A. inter CA3088E. It may headphone or Ioi The concluding appear in nex ki INTEGRATED CIRCUITS ARE BEING USED IN NEARLY ALL fields of electronics, and there is now at least one i.c. specifically designed for use in most of the more common applications. Even when there is no i.c. for a particular purpose, it is often possible to adapt one which has been designed for an allied role. RECEIVER I.C. The receiver described in this article covers three ranges, these being two short wave bands plus the ordinary medium wave band. The nominal ranges covered are: Range 2, 0.515 to 1.54MHz (580 to 194 metres); Range. 3, 1.67 to 5.3 MHz (180 to 57 metres); and Range 4, 5.0 to 15MHz (60 to 20 metres). The Range numbers, 2, 3 and 4, correspond with the numbers of the Denco coils employed. These are plug-in types and the desired waveband is selected by plugging in the set of three coils for that band. The receiver is suitable for the reception of a.m., c.w. and s.s.b. signals. The output is intended for high impedance headphones of 2,000 to 4,000e. An S -meter is included to provide a useful means of comparing signal strengths. An R.C.A. integrated circuit type CA3088E forms the basis of the receiver, and although this i.c. is primarily intended for use in an a.m. broadcast receiver, it functions extremely well in the simple short wave receiver to be described. This i.c. contains almost all the active circuit elements for the receiver, the only additional active device being a silicon transistor. An optional output stage which provides enough signal to drive a speaker may be added. This output stage is described in Part 2, which will be published next month. 672 Y-III" Band-pass rcircuit Mixer -os Ist I.Famp BF254 1 I B.FO L Fig. 1. Block diagram showing the stages of their all active devices are contain; RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com F, RCUIT SUPERHET Part 1 A. Penfold tandard medium wave with two short wave to 20 metres, this 30 rer is designed around :egrated circuit type y be made up either for oudspeaker reception. second article will ext month's issue. Apr 2d Transistor det. I.Famp BLOCK DIAGRAM 6-ó AE amp. High CA3088E HS-meter I.C. driver Z phones 5 -meter Zener A.G.C. stab. circuits A block diagram illustrating the functions of the various stages of the receiver is shown in Fig. L The aerial signal is passed to a conventional mixer-oscillator stage via a band-pass filter tuned to the frequency of reception. This arrangement gives good image rejection. From the mixer-oscillator the signal is passed to the two i.f. amplifiers, and then to a transistor detector. The detected output is fed to a pair of headphones via a 2-stage audio amplifier. A b.f.o. is provided for the reception of c.w. and s.s.b. signals, and its output is coupled to the first i.f. amplifier. The power supplies to the b.f.o., i.f. amplifiers and detector are all stabilized by a zener diode. Apart from providing an audio output, the detector also produces a d.c. bias which is used to drive the a.g.c. and S -meter circuits. A.G.C. is applied to both the first i.f. amplifier and the mixer -oscillator stages. It is not normally advisable to apply a.g.c. to the mixer -oscillator as, amongst other effects, it may cause oscillator detuning, but in this simple design there is no r.f. stage to which a.g.c. could be applied, and so the a.g.c. coupling to the mixer-oscillator was tried. No adverse effects at all have been noticed, and it results in an extremely flat a.g.c. characteristic. INTERNAL CIRCUIT The internal circuit of the CA3088E appears in Fig. 2. J receiver. Apart from the mixer-oscillator transistor, tined inside the integrated circuit tie J UNE As may be seen, the i.c. incorporates 14 transistors, 23 resistors and 6 diodes. One of the diodes is a zener type. R3 to R6, D1 to D4 and TR2 to TR4 provide two stable voltage sources which are used to bias the base of TRI via Rl and that of TR5 from the emitter of TR4. TR1 would normally function as a converter, or mixer - 1975 673 www.americanradiohistory.com Converter output 2nd I.F. input c3 98 10 Converter input 1st I.F. Ist input 04 output 96 oV+ I.F. 15 TRI o 2 TR7 TR5 Converter R22 TRIO TR9 TRI2 bypass 9 R13 R16 R14 Detector output 7 2nd I.F. bias eR20 ZD1 16 R7 TR6 R23 R18 R D2 o V+ R19 TR2 R R21e TR3 TRI D3 615 A.F. D4 R10 65 Substrate 613 RI 11 R.F. A.G.C. A.G.C. output filter output a 14 12 Tuning A.F input meter output Fig. 2. The internal circuitry of the i.c. type CA3088E Rearside view of the receiver. The i.c. component panel is to the right, above the chassis oscillator, but it is a little difficult to couple it to an oscillator coil of the type required for the present receiver. In consequence, an external mixer-oscillator transistor is employed, and TRI is brought into use as a b.f.o. TR5 is the first i.f. amplifier, and is used in the common emitter mode of operation. TR7, TR9 and TRIO constitute the second i.f. amplifier, with TR7 and TRIO as emitter followers and TR9 in the common emitter configuration. Detection of the i.f. signal is provided by TR12, which is biased close to cut-off. Unlike most transistor detectors it offers no voltage gain, as it is connected as an emitter follower. On the other hand, it gives a very low level of distortion. The signal at the emitter of TR12 can be coupled to an external i.f. filter and the receiver volume control. The voltage at the emitter of TR12 is coupled also, via R20 and R19, to an external a.g.c. filter capacitor, which can be a relatively high value electrolytic component. This bypasses to chassis any a.f. or i.f. signal which might otherwise be present and allows an a.g.c. voltage to be produced. The voltage is fed direct to the base of TR11, an emitter follower, whose emitter may be coupled to a tuning meter. In the present receiver it connects to the S -meter. The a.g.c. voltage is applied also to the base of TR6, the collector of which connects to the junction of R7 674 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com COMPONENTS Resistors (All fixed values + watt 5%) RI R2 R3 R4 R5 R6 R7 R8 R9 RIO R 11 R12 R13 R14 R15 R16 R17 VR1 VC5 8.2k52 68052 4.7k12 1.5k12 1.5k52 VC6 15052 Inductors VC7 2.7kû (L1, L2, L3 all Denco Miniature Dual Purpose coils, transistor usage) L1 Blue coils, Ranges 2T, 3T and 4T L2 Yellow coils, Ranges 2T, 3T and 4T L3 Red coils, Ranges 2T, 3T and 4T 4.7k12 4.7k52 22052 47052 1.5k52 5.6k52 IFTI IFT2 1.2M52 2.7k52 3352 56052 10k52 potentiometer, IFT3 log track, with C14 C15 C16 C17 C18 C19 C20 C21 C22 C23 C24 VC1 VC2,3,4 10pF silvered mica or ceramic 10pF silvered mica or ceramic 0.01µF plastic foil or disc ceramic 100µF electrolytic, 6 V. Wkg. 0.047µF plastic foil or disc ceramic 350pF silvered mica (see text) 1,100pF silvered mica (see text) 3,000pF silvered mica (see text) 27pF silvered mica 0.01µF plastic foil or disc ceramic 1,000pF polystyrene or silvered mica 0.022µF plastic foil 0.1µF plastic foil 0.01µF plastic foil 0.01µF plastic foil 100µF electrolytic, 6 V. Wkg. 0.01µF plastic foil 10µF electrolytic, 10 V. Wkg. 0.22µF plastic foil 1251.1F electrolytic, 10 V. Wkg. 0.01µF plastic foil 0.022µF plastic foil 10µF electrolytic, 10 V. Wkg. 1.8pF silvered mica or ceramic 25pF variable, type C804 (Jackson Bros.) 310 +310 + 310pF 3 -gang capacitor, type E3 (Jackson Bros.) and R8 in the bias feed to the first i.f. amplifier, TR5. As signal strength at detector TR 12 increases, this transistor passes more current, whereupon its emitter goes positive. In consequence, so does the base of TR6, with the result that its collector goes negative, reducing the bias current available for TR5 and, hence, its gain. An a.g.c. loop back to the first i.f. amplifier is thus set up. TR8 functions in the same way as TR6 but, in this instance, the collector couples to an external bias circuit at the r.f. amplifier or, with the present receiver, the mixer -oscillator. A.G.C. is, therefore, applied to the controlled external stage as well. JUNE (Denco) i.f. transformer type IFT18/465kHz (Denco) BF254 Integrated Circuit CA3088E (R.C.A.) Capacitors C2 C3 C4 C5 C6 C7 C8 C9 C10 C11 C12 C13 i.f. transformer type IFT14 (Denco) i.f. transformer type IFT18/465kHz Transistor TRI S2 Cl 25pF variable, type C804 (Jackson Bros.) 5pF variable, type C804 (Jackson Bros.) 15pF variable, type C804 (Jackson Bros.) Meter MI S -meter, Radio) Switches Si S2 Sockets SK1,2 JK1 Henelec 38 Series (Henry's -pole 2 -way miniature rotary (see text) 1 s.p.s.t., part of VRI wander plug sockets 3.5mm jack socket Battery 9 -volt battery type PP7 (Ever Ready) Miscellaneous 8:1 tuning drive, 2 in. type T502 (Eagle) 6 knobs Headphones (2,000 to 4,00052) 3 B9A valveholders Chassis and front panel (see text) 3.5 mm. jack plug Battery connectors S.R.B.P. panel, 41 x 31 in. Trimming tool type TT5 - see text (Denco) Bolts, nuts, wire, etc. TR13 and TR14 form a simple 2 -stage a.f. amplifier which is isolated from the other circuits. TR13 is a common emitter amplifier feeding into the emitter follower, TR14. An a.f. output can be taken from the emitter of TR14. The final component to be considered is the zener diode, ZD1. This provides a stabilized voltage at a nominal level of 5.6 volts. The requisite series resistor is external to the integrated circuit. The CA3088E may be obtained from Ambit International, 37 High Street, Brentwood, Essex, CM14 4RH. 1975 675 www.americanradiohistory.com RECEIVER INPUT VC6 offers fine tuning of the oscillator and operates as a bandspread control on the short wave bands. Power is applied by way of the r.f. decoupling components, R5 and C10. The BF254 specified for TRI is available from Electrovalue Ltd., 28 St. Judes Road, Englefield Green, Egham, Surrey, TW20 OHB. Fig. 3 shows the circuit of the input stages of the receiver. Although no r.f. amplifier is used ahead of the mixer -oscillator, TRI, the circuit still incorporates two tuned circuits resonant at signal frequency. These are loosely coupled by C24. The coils are tuned by VC2 and VC3, these being ganged with the oscillator tuning capacitor, VC4. VCl and VC5 are separate variable capacitors which provide fine tuning of the input tuned circuits. It will be noted that no connection is made to one of the windings of both L1 and L2. TR1 is biased by R1 and R3, with a.g.c. from the integrated circuit being applied via R7. C4 ensures that there is a complete absence of a.f. on the control voltage applied to TRI base. The mixer -oscillator stage is quite conventional and uses a familiar oscillator configuration. R2 and R6 are included in circuit to prevent instability at the high frequency ends of the bands covered. C6, C7 and C8 are the padding capacitors for each band. They connect to different pins of the valveholder into which L3 is inserted, and are automatically selected since each oscillator coil has its tune winding returned to the pin corresponding to its I.F. AN D DETECTOR STAGES The circuit of the remaining stages of the receiver is reproduced in Fig. 4. An i.f. transformer, IFT1, is used as the b.f.o. oscillator coil and this couples to the base of TR1 inside the i.c. (Fig. 2 transistor nun.bering) via C11 and R8. The transistor is employed in the emitter follower mode, whereupon its emitter is in phase with the base and there is slightly less than unity voltage gain. The emitter couples via C12 to a tap in the i.f. transformer tuned winding, and the consequent step-up in voltage is sufficient to provide oscillation. No con, nection is made to the untuned winding of the i.f. transformer. VC7 is the b.f.o. frequency control, and the positive supply is obtained by way of decoupling components R9 and C14. S1 is the b.f.o. on -off switch. There is no direct connection between the b.f.o. and i.f. amplifier stages, and the b.f.o. is coupled into the i.f. amplifier by stray capacitances. This provides an adequate level of b.f.o. injection which is, at the same time, not so excessive as to produce a high a.g.c. voltage. The S -meter connects directly between pin 12 of the i.c. and chassis with the polarity shown. C16 is the a.g.c. filter capacitor. The rather high value of 1001.1F specified for this capacitor is quite in order as the a.g.c. circuits padding capacitor. The padding capacitors have slightly unusual values and some difficulty may be experienced in obtaining these as single components. It is quite in order to make them up with two capacitors in parallel. For instance C8, specified as 3,000pF, can consist of two 1,500pF capacitors in parallel. The padding capacitors should have a tolerance on value of 5% or better. Pos. from I.F. R5 panel 3 o I.F. output 0 2 8 (red) (yellow) L3 9 L2 8 = C24 RR TRI BF254 vClO R2 5 I 7 I C2 al 2 0 VC5 C3! 6 'IÌip jllp I dl R R4 Y 3 40 Y T7T TCB ouo) R7 4-ffle--E.-A.G.C. L 1 C9 from bec I.C. J BF254 Lead -outs Fig. 3. The aerial input and mixer-oscillator circuits of the receiver RADIO & ELECTRONICS CONSTRUCTOR 676 www.americanradiohistory.com S2 2 1 R0 Pos. to R12 o MAN` mixer-osc. r r3 From mixer-osc. CI7 ;I --b +9V L_ 4' i I11 T T2z11 0 I Si 61 J 1 IFT2 1FT3 CI5 R9 C14 l 10 7 8 B.F.O. IFT1 16 VR1 A.G.0 to 13 R7 II 12 15 cl6 w R13 o Fig. 4. The i.f., b.f.o., detector and a.g.c. stages of the receiver. As will be seen, a number of chassis connections are carried by the transformer screening cans it inside the i.c. are at low impedance. A capacitance of The use of double -tuned i.f. transformers means that 50µF is suggested by R.C.A. for the normal broadcast there are four tuned circuits in the i.f. amplifier, wherereceiver application, but it was found that a slightly upon quite sharp selectivity is achieved. Resistors R10, higher value was required to prevent slight instability on R11 and R16, and capacitors C17 and C20 are all strong signals. supply decoupling components. R12 causes the supply The output from the mixer-oscillator stage of Fig. 3 voltage at the first i.f. amplifier output to be slightly couples to the primary of IFT2, and the secondary of reduced. this transformer passes the signal to the input of the C22, R17 and C13 filter out the i.f. content of the first i.f. amplifier in the integrated circuit. C15 bypasses detected signal, leaving the required audio signal, which the earthy end of the secondary winding to chassis is applied to volume control VR1 via C19. The slider of without upsetting the bias conditions for the i.f. the volume control then couples to the input of the a.f. amplifier transistor. IFT3 couples the output of the first amplifier in the i.c. via C23 and R15. R14 is a bias i.f. amplifier to the input of the second i.f. amplifier. resistor, coupling the emitter of TR14 back to the base Bias current for the second i.f. amplifier input is taken' of TR13 (both transistors inside the i.c.). The a.f. output from pin 7 of the i.c. to pin 8 via the i.f. transformer is fed to a phone jack socket via the d.c. blocking secondary. The biasing is stabilized by a high level of capacitor C18. S2 is the on -off switch and is ganged d.c. negative feedback, but there is no feedback at the with VR1. intermediate frequency because of the bypass provided. The maximum audio output signal level approaches by C21. In consequence, the full gain of the second i.f. 1 volt r.m.s., which is perfectly adequate for a pair of high impedance headphones. amplifier is achieved. JUNE 677 1975 www.americanradiohistory.com METALWORK The front panel is cut out from 18 s.w.g. aluminium sheet. Drilling details for the front panel, together with details of the other main metalwork are given in Fig. 5. Most of the drilling is quite straightforward. The large cut-out for meter M1 can be made with a fretsaw or a coping saw fitted with a blade having fine teeth, and the a in. diameter hole for the tuning drive can be made with a e in. chassis punch. (If it is desired to have this last hole very accurately positioned, it can be marked up and cut out after the other holes in the panel and chassis have been drilled. The panel and chassis are temporarily assembled, and VC2, 3, 4 is placed on the chassis surface with its spindle against the rear of the panel. The height of the centre of the 4 in. hole can then be marked off from the capacitor spindle, after which the panel and chassis are disassembled and the e in. hole cut out). The four smaller mounting holes for meter M1 are drilled 6BA clear using a No. 31 drill. Their positions may be marked out, after the large hole has been cut out, with the aid of the meter itself. There are two small mounting holes for the tuning drive, and these are located and drilled as described later. The chassis is best obtained ready made, and is available from H. L. dmith & Co. Ltd., 287-289 Edgware Road, London, W.2. It is in Style `K', measures 82 by 52 by 2 in., and is made of 16 s.w.g. aluminium. For clarity, the chassis is shown in Fig. 5 with its sides opened out. FRONT PANEL y 11/26 13/4" I q VC7 5" 11/2` dia I i 1/40 VRI JK1 o n o VC5 VC1. VC6 24 900 bends 27/8° 3/4" s/8" i I I/4° 51 Ì =r15/8e-I` 15/ 8e dia.Ì O I" dia VC2,3,4 â e â-metcr 3/8dia 3/8 %2° dia I8"~ 6BA clear 3/8"dia 81/2" SCREEN The components and wiring under the chassis Again, most of the drilling is quite straightforward. The three mounting holes for VC2,3,4 are drilled 4BA clear with a No. 24 twist drill. The thrèe holes between these mounting holes allow leads from the fixed vane tags to pass through the chassis. There are a further three holes for wires alongside the component panel outline. The sizes and precise positions of these six holes are not critical. The component panel, which will be fully described in next month's issue, can be initially cut out at this stage, and it consists of a piece of f'j in. s.r.b.p. (`Paxolin') sheet measuring 41 by 3$ in. Four 6BA clear holes are drilled at the extreme corners, after which it is used as a template for marking out the four corresponding 6BA clear holes in the chassis. The component panel may then be put on one side for later use. As can be seen from the photograph of the chassis underside, an L-shaped aluminium bracket holds the battery in place on the side opposite the three valveholders. This bracket, whose actual dimensions and unimportant provided that it holds the battery securely, may next be made up. It is secured to the chassis side by two 4BA bolts and nuts. The holes for these may be drilled in the bracket and chassis side. SCREEN I 44°din 2" 4. SK2 ra,'6BA'", SKI clear `I+ 11/4" 4BA hBe ÿC4l clear 3/odia s 41/4" Component __ panel 1 bbs hols 1_/8"---1I/24- V JKI I/4"dia 51/2" 68A lear YC21e 3/8°dia I" 9/16° I V VC 4BA clear To improve stability, a vertical screen is placed between L2 and L3. The dimensions of this are given in. Fig. 5, and it is made of 18 s.w.g. aluminium. Start by cutting out a piece of aluminium measuring e by 2s in. Then make two hacksaw cuts, each a in. deep and each e in. from, and parallel with, the 2g in. edges. Use a sharp modelling knife to make a deep score in the metal between the inside iends of the cuts, and then repeatedly bend the piece of metal between them backwards and forwards until it breaks off. This leaves the shape shown in Fig. 5, which can next be bent and drilled as indicated. It is used as a template to mark out the corresponding two 6BA clear holes in the chassis, which are then drilled. When all possible drilling is complete, the chassis and front panel are temporarily assembled by the mounting nuts of JK1 and one or more of the lower row of controls. It will probably be necessary to shorten the spindle of the 3 -gang tuning. capacitor slightly so that, -VC e CHASSIS Fig. 5. The dimensions of the front panel, chassis and screen. The positions of undimensioned holes are discussed in the text 678 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com when it is mounted, none of the spindle extends beyond the front panel. The spindle must, of course, be cut with great care to ensure that there is no damage to the capacitor. The capacitor is then secured to the chassis with three short 4BA bolts. The tuning drive is next placed on the spindle and the positions of the two small holes marked on the front panel with its aid. The front panel and chassis are then disassembled and the two holes in the panel drilled out 6BA clear. The drive is supplied with a short bolt which screws into a threaded hole at the top. This third mounting bolt was not found necessary, and no hole was drilled for the bolt. NEXT MONTH ly will be described. For completeness, a full Components List for the receiver (apart from the a.f. output stage) accompanies this article. References to some of the parts must, of necessity, be kept to the next article, which will clear up any outstanding points concerning the components. Readers who intend building the receiver complete with the a.f. output stage may prefer not to obtain the headphones specified. The receiver headphone output could also be applied to an external amplifier. It is, however, probably more convenient to bring the receiver into working order with headphones first, after which the use of the optional a.f. stage or an external amplifier may be taken into consideration. In next month's issue, details will be given of assemband wiring up. Also, the optional a.f. output stage (To be concluded) Trade News TV SOUND CHANNEL An i.c. which provides all the active devices for a TV sound channel, including the a.f. output stage, is announced by SGS-ATES, whose U.K. distributors include ITT Electronic Services, Harlow. The functions provided by this i.c., the TDA1190, are i.f. amplifier and limiter, active low-pass filter, f.m. detector, d.c. volume control and power output amplifier. The limiting voltage is 30µV and the i.c. can operate at any i.f. between 4.5 and 6MHz. It has a high input impedance and can, in consequence be fed via a ceramic filter or tuned circuit. The a.c. gain of the unit is determined by the value of an external fixed resistor. The a.f. output is typically 4.2 watts into a 1652 speaker at 10 % distortion with a 24 volt supply. Distortion falls to 2 % at 3.4 watts typical and to 0.55 % typical at 50mW under the same conditions. There is no frequency radiation, whereupon there is no necessity for screening. The TDA1190 is in a 12-pin quad in line plastic package with two protruding tabs at the centre which are soldered to a heat sink. The latter can be provided by an area of copper on the p.c.b. on which the i.c. is mounted, or by a simple folded metal sink. The photograph shows the i.c. mounted on a printed circuit board complete with all external components, including the volume control which will normally be. fitted to the receiver front panel. The square screening can contains a quadrature coil. QUAD 741 Four 741 op -amps in a single 16 pin d.i.l. package. This new Raytheon i.c. is stocked by Jermyn Distribution, Sevenoaks, Kent INPUT (A) - INPUT (0) -INPUT (A) ,-INPUT (0) OUTPUT (A) OUTPUT (0) OUTPUT (B) *VCC +INPUT (B) OUTPUT (C) -INPUT (B) =INPUT IC) GROUND INPUT RC 4136 DP (Top View) C One of the most popular operational amplifiers available these days is the 741, which has the advantages of requiring no external frequency compensating components together with an output which may be short-circuited to earth or either power supply rail without damage. A development of the 741 has now been introduced by Raytheon. This, the 4136, consists of four 741 amplifiers contained in a 16 pin d.i.l. package. The accompanying illustration shows the appearance of the 4136 and its pin allocations. The four independent amplifiers in this i.c. meet, or in some cases exceed, A complete television sound channel incorporating the SGS-ATES integrated circuit type TDA1190. This includes the a.f. output stage which drives the speaker standard 741 specifications, and channel separation is no less than 105dB under open -loop conditions. The amplifiers are all on a single silicon chip with the result that there is good parameter tracking over a wide frequency range. The power supply required is 15 volts positive and negative, and this may be provided by a Raytheon 4194 dual tracking voltage regulator. The latter is capable of supplying up to forty-five 4136 i.c.'s, which corresponds to a total of 180 operational amplifiers. Both the 4136 and the 4194 have the prefix RC or RM according to whether they meet commercial or military temperature specifications. There is also a choice of package styles. U.K. distributors are Jermyn Distribution, Sevenoaks, Kent, who stock all versions of both the 4136 and the 4194. 679 www.americanradiohistory.com THE WHEATSTONE TELEGRAPH By D. P. Newton A few simple parts and a little ingenuity are all that are needed to recreate a signalling instrument which originally appeared more than a century ago. A stone HUNDRED YEARS AGO THIS YEAR CHARLES WHEAT - died at the age of seventy-three, yet that for which he is remembered - the Wheatstone bridge was not even his idea. Samuel Hunter Christie, a mathematician older than Wheatstone, mentioned that it should be possible to `balance' four resistors by such a circuit and the more practical Wheatstone turned the idea into a useful reality and popularized it. TELEGRAPH It is ironic that the very thing for which Wheatstone was famous in his own time, the telegraph, did not bear his name. Again, the basic idea was not his own. It was brought to him from Germany by Cooke, but he greatly improved on it. It was only a few years earlier, in the 1820's, that the deflection of a compass needle by a wire carrying a current had been found. Wheatstone's telegraph worked on this principle, which is illustrated in basic form in Fig. 1. With five needles he found he could point pairs Magnetic needles / Fig. 2. Here there are five needles which may be deflected in either direction. The second and fourth needles have been deflected to indicate the letter "S' Wire Magnetic north Compass Line of force MAGNETIC NEEDLES Direction of current Fig. A compass needle is deflected when current passes through a wire below it 1. of them at any of the important letters of the alphabet. Thus, in Fig. 2, 'S' lies at the point of intersection of the two displaced needles. The wires underneath these needles carry an electric current and have magnetic lines of force around them, as in Fig. 1. These lines of force interact with the magnetic needles. In fact, it is easy to make a model telegraph similar to that of Wheatstone. The most difficult task is to make and balance the magnetic needles. Of course, five cheap compasses would be the easiest solution, and if it is decided to buy them then this step is omitted. a Out of thin tin sheet, such as is used in a biscuit tin, cut and shape five needles as in Fig. 3. With a nail punch make a depression at the balancing point. Magnetize each needle by rubbing a magnet along it in a loop about fifty times, as in Fig. 4. If a magnet is not available, one may possibly be obtained from an old loudspeaker or TV tube focus assembly. 680 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com 5 balanced needles 1cm 1 Magnetic north c 6 i T 11 Fig. 3..A home-made magnetic needle can be cut out from thin tin-plate, as here 0 2 0 Magnet 0 0 3 4 0 5 Fig. 6. The telegraph receiver. Five parallel wires pass under the needles and are connected together at the top Needle Fig. 4. The needle is magnetised by being continually stroked in one direction with a magnet Brass pin Cork THE TRANSMITTER Five brass screws, with one transmitting wire connected to each, are fixed on a small wooden board as shown in Fig. 7. Corresponding wires 1, 2, 3, 4 and 5 are connected over the required distance of transmission between the transmitter and receiver. Mark on the letters at the transmitter as shown. In this working Notch Fig. 5. A mounting pivot for each magnetic needle can be made with a brass pin and a cork 5 brass screws The support for each needle is the point of a brass pin, of the type used in dressmaking, fitted in a cork as in Fig. 5. Cut a notch on the underside of the cork to allow a wire to pass underneath. Try balancing the needle; it is unlikely that this will be successful at first, especially after the needle has been magnetized. Redress any unbalance by sticking adhesive tape on the lighter side. The wooden board for the receiver should be large enough to allow each needle to settle north -south without too much mutual interference. For needles of the size of Fig. 3, a spacing of 10 to 12cm. between each is adequate. Smaller needles can be placed closer together. Onto the board fasten five parallel wires, each running under a needle and all connected together along the top, as in Fig. 6. Securely glue the corks in place. Mark on the letters as in Fig. 2. Note that only twenty positions are available, so some letters are omitted. Turn the board to face north. JUNE Plugs 4-5V I 47n watt Fig. 7. The transmitter. The two plugs are applied to the appropriate screws for each letter with the 1975 polarity indicated 681 www.americanradiohistory.com model a 4752 resistor is inserted in series with one of the battery leads to limit the current drawn from it to around 100mA and thus prolong battery life. If there were very long leads between the transmitter and the receiver, the resistance in these would alternatively keep battery current to an acceptable level. The battery may be an Ever Ready No. 126 `Bell' type, or similar. The signal is transmitted by holding the plugs from the battery onto the appropriate screw heads. Thus, to transmit letter 'N' place the positive plug onto screw 4 and the negative plug onto screw 1. This sends the current in opposite directions under the two needles for 'N' and deflects them the opposite way to point at the letter. Polarity must be observed, at the transmitter screws -since this -determines whether letters are selected above or below the needles. For the missing letters it is easy to improvise. ASTATIC NEEDLES Of course, Wheatstone's telegraph was more sophisticated. For example, he did not have to worry about lining it up along the north -south line. This problem he overcame by using astatic needles, that is, pairs of needles which are unaffected by the earth's magnetic field. Wheatstone's inventive genius did not end here. As well as his telegraph, patented in 1837, he invented the concertina and stereoscope, and we owe the word `microphone' to him although this was coined for a non -electrical device which arose from some experiments with sound. With the advent of the railways, he could anticipate the success of his telegraph. Its simplicity of operation, as demonstrated by the model, was so attractive that it remained in use until the early years of this century. SOLDERING IRON SA V ER By P. Thomas The life of NE OF a soldering iron can be considerably extended if it is run at half power when not in use. THE FIRST THINGS MOST OF US DO WHEN settling down to a spell of work at the bench is to switch on the soldering iron. If the iron is used fairly continually it is then able to maintain a reasonably constant temperature. If on the other hand it is used only infrequently it can take up a higher than average temperature,'whereupon both element and bit life are needlessly reduced. 2 To A.C. mains soldering Silicon 1 SERIES RECTIFIER Switch positions What is required here is a switching circuit which allows the iron to run at reduced power whilst not in use, so that it can be brought up very quickly to operating temperature whenever it is required. The result will be an extended soldering iron life with the added facility that the iron can be brought into use very shortly after it has been switched to full power. All that is needed is a silicon rectifier in series with the a.c. supply to the iron, as indicated in the accompanying diagram. When the switch is closed both mains halfcycles are applied to the iron and it operates in normal manner. When the switch is set to the `half power' position the rectifier is in series with the iron and only alternate half-cycles of mains current are applied to it. In consequence, it runs at a reduced temperature. The author will be the first to agree that the use of a series rectifier in this manner is not a new idea. Nevertheless, it is one which quite a few constructors do not appear to have heard about. iron rectifier I - Half power 2- Full power 'half power' position when the soldering iron is not required. Setting the switch to 'full power' causes the iron temperature to rise very quickly to normal working level The switch is set to the Since the soldering iron represents a resistive rectifier load without a parallel reservoir capacitance, the minimum p.i.v. rating of the rectifier needs to be only 1.414 times the r.m.s. mains voltage. With 240 volt mains, this works out as 340 volts. The current drawn by the soldering iron will be quite low. For instance, a 25 watt 240 volt iron will draw a little more than 0.1 amp only. A 1 amp silicon rectifier with a p.i.v. rating of 400 volts, such as the 1N4004, would be quite adequate in the circuit. Since the 1N4004 is a very small component it could be wired directly across the switch. Any other silicon rectifier with similar or higher ratings could also be employed. 682 www.americanradiohistory.com RADIO & ELECTRONICS CONSTRUCTOR THE 'SLIDE RULE' RECEIVER CUM CAPITANCE METER Part By Sir Douglas Hall, K.C.M.G. 2 This concluding article describes the Fablon having approximately the same outside dimenshould be stuck to the plywood before the tagwiring and calibration of the earphone sions is screwed down, to keep the tag undersides version of this unusual design, and strip insulated from the wood. Small woodscrews pass then gives details of the added a.f. through the holes in the third tag from the left and the stage required for loudspeaker re- second from the right, both of which are earthy so far as ception. r.f. is concerned. Next to be fitted are VR1/S2, S1 and the earphone jack socket. It may be necessary to temporarily remove the Perspex panel at the top to enable these parts to befitted. Fig. 7 shows a slide switch, but the same connections will be required if a toggle switch is employed instead. Next wire up the small components, as illustrated. For clarity these are shown spread out in the diagram but in practice they should be connected up with reasonably short leads and no part should be outside the `chassis' depth, as defined by the two 1 in. side pieces. Take care to connect to the correct tags of the earphone 'socket. If any doubt exists here, refer to the circuit diagram of Fig. 1 and identify the appropriate tags with a continuity tester or ohmmeter. VC1 is held in place by two stiff wires which also connect it to the test terminals. In the prototype it was positioned over the slide switch. IN LAST MONTH'S ARTICLE DETAILS WERE GIVEN OF circuit operation, and the initial steps in the construction of this receiver were covered. We pass on next to the process of wiring up. WIRING An 18 -way tagboard was specified in the Components List which appeared last month, and this is the R.S. Components `Standard' tagboard. An 11 -way tagstrip is cut out from this tagboard, and is secured to the inner top surface of the receiver (i.e. to the underside of the Fig. 2(b) item) in the manner shown in Fig. 7. A piece of R4 L2 -1-TR2 -R6_ TR case LI PP 3 C B _CZ C A . o 0 r- VCI SKI Test terminals Fig. JUNE 7. Wiring of the receiver in its earphone -only version 683 1975 www.americanradiohistory.com output stage and loudspeaker have been added The receiver when the a.f. However, the question of obtaining suitable calibration capacitors is left to the reader, who may already have a good range of values in his spares box. Setting up the receiver for capacitance calibration is as described in the previous issue. The first scale may be from zero to 56pF using Radio 1, the second from 56pF to 560pF using Radio 3, and the third from 560pF to 5,000pF using Radio 2. Remember that the zero pF point is that at which Radio 1 is received with no capacitor across the test terminals. If any difficulty is experienced in identifying Radios 1, 2 or 3 when measuring unknown capacitors it is helpful to temporarily remove the capacitor under test and tune in the station required in the normal manner to find what programme is being put out. As. indicated earlier, it may be necessary to adjust VC1 from time to time. This can be done through a hole in the bottom of the case, and the need for the adjustment will be apparent whenever the pointer fails to be at the zero pF position when Radio 1 is tuned in with S I central and no capacitor across the test terminals. SIMPLE CASE SETTING UP Setting up the receiver is a simple process. Fit the PP3 battery, plug in the earphone, set S1 to the central position and switch on. Do not connect any capacitor to the test terminals. Set the ferrite rod so that it is about in. from full insertion into the coil. Adjust VC1 with an insulated trimming tool until Radio 1 is tuned in, using VR1 to give critical reaction. The hands should be kept away from the left-hand side of the receiver when setting up VC1, to avoid hand capacitance effects. The final setting in VC1 will be near its minimum capacitance. If necessary, slide the rod a little further out of the coil to find the Radio 1 Signal. The position taken up by the pointer for Radio 1 will represent zero pF on the first capacitance scale. Three capacitance scales and three tuning scales need to be marked out on the white card which will be positioned under the pointer. As the card is only 1 in. wide the scale lines will be quite close together and small figures will be required. A mapping pen may be used for the final scales. With SI in the centre position, coverage will be from about 120 to 250 metres. When Si is set to bring Cl into circuit there will by medium wave coverage from about 190 to 550 metres, and with S1 set to bring C2 into circuit the band from 550 to 1900 metres can be received. Plenty of stations will be received after dark to assist in calibration if no signal generator is available. Calibration of the capacitance scales is carried out by noting the position of the pointer with capacitors of known value connected to the test terminals. It is suggested that a tolerance of 5% in these would be adeiquate, although obviously the calibration will be more accurate if closer tolerance components are employed. Silvered mica capacitors are particularly suitable as these are normally close tolerance types. Hi -K ceramic. capacitors should not be used for calibration purposes as these normally have a very wide tolerance, but the lower value ceramic types, below some 150pF or so, normally have reasonably close tolerances. The range of calibration capacitances can be increased by connecting capacitors in parallel or series. A particularly useful range would be given by capacitors having the individual values of 1pF, 2.2pF, 4.7pF, 10pF, 22pF, 47pF, 100pF, 220pF, 470pF, 1,000pF, 2,200pF and 4,700pF. If the receiver is to be used as an earphone -only set it can be housed in a simple case, and a suggestion for this is given in Fig. 8. The four sides are made of ; in. plywood and the base of s.r.b.p. or Formica. Small woodscrews are used to fix the pieces together and the whole is covered with Fablon or Contact. Check the exact measurements of the receiver `chassis' before making the case, and make any necessary amendments to the dimensions given in Fig. 8 that are required in practice. Discrepancies from nominal dimensions can result from slight inaccuracies in the cutting of plywood, or in the use of plywood which is not exactly ; in. thick. The current drawn from the PP3 battery by the 2 transistor receiver is only 350µA, and so battery life will be very long. Something of the order of 1,000 hours can be expected from a new battery. 11/2` I/2"hole for adjusting VC) r 341i23it _J 63/4" L1. Fig. 8. A simple case for the receiver may be constructed along the lines illustrated here RADIO & ELECTRONICS CONSTRUCTOR 684 www.americanradiohistory.com Test terminals SKI ----- ---- Speaker frame scraped clear of enamel 23/4" Centre lead -=6lie Fig. 9. How the a.f. output stage is assembled and wired A.F. SECTION As so far assembled the receiver has been built up to the phone socket in the circuit of Fig. 1, which was published last month. If. it is desired to include the a.f. output stage shown to the right of the broken line in that diagram, construction may proceed in the manner next to be described. No modification is made to the wiring that has already been carried out and the receiver may still be used with the earphone when desired. The only change is that the aluminium or tinplate clip which held the PP3 battery is not required in the loudspeaker version. The current consumption of a transistor in the TR3 stage is typically 10mA and so a larger PP6 battery is employed instead of the PP3. The PP6 uses the same type of connector, as the PP3 battery. A 5 -way tagstrip and a 2 -way tagstrip, both cut from the 18 -way groupboard, are now secured to the underside of the plywood piece of Fig. 2(b) in the manner shown in Fig. 9. Note that the lugs of are soldered to a tag on each strip and that the strips should be positioned to allow this. The 5 -way tagstrip is secured with small woodscrews passing through the holes in the second and fifth tags from the left, and the 2-way tagstrip by a small woodscrew passing through the hole in JUNE 1975 the left-hand tag. Pieces of Fablon should be stuck to the plywood before securing the tagstrips, to insulate the tag undersides from the wood. A piece of s.r.b.p. is cut out to form the speaker baffle and this has the shape and dimensions, apart possibly from the 2i in. height dimension, which are shown in Fig. 9. It has been the author's experience that most speakers described as 5 by 3 in. have actual outside dimensions of about 5i by 2â in., and the 2 in. height dimension given in the diagram assumes that a speaker of this type is employed. If the speaker to be used happens to be larger along the nominal 3 in. dimension, then the height of the s.r.b.p. panel should be increased accordingly. The panel is secured to the receiver, as so far assembled, by passing the test terminal screws through the two 6BA clear holes at the top. The s.r.b.p. panel is secured immediately under the Perspex panel, and thereby provides some of the spacing previously given by the spacing washers here. Smaller spacing washers below the s.r.b.p. may still be required to space off the Perspex panel correctly. The s.r.b.p. panel requires an aperture for the speaker and four holes for the speaker mounting bolts. A solder tag is fitted under one of the mounting nuts, and the speaker frame is scraped clear of enamel at this point to enable 685 www.americanradiohistory.com MA/NS By N. R. Wilson IT The additional parts for the a.f. stage and speaker are affixed quite simply to the earphone version of the receiver a good connection to be made. A 6-way tagstrip, again cut from the 18 -way tagboard, is soldered to the speaker tags as shown, and the lugs of T2 are soldered to two other tags on the strip. Additional wiring is carried out as illustrated in Fig. 9. The frame of Ti carries the negative supply connection from the emitter of TR3 to its own green lead and to the 6-way tagstrip on the speaker. When the a.f. section has been completed, the black and white leads from Ti should be tried first one way round and then the other. If these leads are connected in the wrong phase there may be instability. When the earphone plug is inserted, the output stage is completely cut off since its negative supply is then disconnected. If, however, the plug is inserted when the receiver is switched on, signals will still be heard from the speaker for a few seconds until capacitor C11 discharges. The earphone socket circuit now causes a standing direct voltage to appear across the earphone, but this caused no difficulty with the prototype. The direct voltage may be removed, if desired, by inserting a 0.2211F capacitor between the phone socket and the red lead of Ti. This is only a suggestion, however, and has not been checked out on the prototype, which performed quite satisfactorily with the circuit as shown. A case for the loudspeaker version of the receiver may be made up on the same lines as that shown in Fig. 8, having an s.r.b.p. or Formica base, and plywood sides. The 2â in. sides will now extend up to 52 in., and the base has its 3i in. dimension increased to 6 in. These new dimensions will need to be longer if a larger speaker is used, and the final dimensions should in any case be taken from the actual receiver, as built. The case will not need the 1 by in. cut-out shown in Fig. 8. The four side pieces may need to be wider than 1 â in. to accommodate the speaker and the battery, and this point has to be checked in practice with the actual speaker and battery before commencing work on the case. (Concluded) IS OCCASIONALLY DESIRABLE TO PROVIDE A POSITIVE means of warning that an a.c. mains supply has cut off. Such a facility can be useful when the supplied equipment does not give audible or visual indications to show that it is turned on. A mains failure monitor can also be useful when soak testing intermittent television receivers and the like when these occasionally blow their main fuses. A very simple mains failure monitor consists of a relay which is energised by the mains supply. On cessation of the supply the relay then de -energises and a pair of its contacts complete a circuit between a battery and a bell or buzzer. The only real disadvantage with this approach is that the battery is needed, and batteries tend to be neglected or forgotten if they are used only infrequently. CHARGED CAPACITOR The unit to be described here does not require a battery. Instead, a large value electrolytic capacitor is charged when the mains supply is available. As soon as the mains supply cuts off, the charged capacitor feeds into an audio oscillator coupled to a loudspeaker. The oscillator then starts to run and continues until the capacitor has discharged. The resultant sound, although present for a short time only, should be sufficient to attract attention to the cessation of the mains supply. The circuit of the monitor appears in the accompanying diagram. In this, the audio oscillator incorporates the unijunction transistor, TR2. A unijunction transistor is employed because, apart from the small standing current which flows between the base 2 and base 1 5f the device, nearly all the current drawn is converted into the pulses which appear in the emitter and base 1 circuit. A unijunction oscillator is, in consequence, reasonably efficient and can give a relatively high output without, in the present case, too rapidly discharging the electrolytic capacitor which supplies it. If TR is ignored for the moment, the circuitry around TR2 functions as a standard unijunction transistor oscillator in the following manner. When a supply voltage is present, C2 charges via R3 until the voltage on its upper plate reaches the emitter triggering level, whereupon it discharges rapidly via the emitter and base 1 into the speaker. The voltage across the capacitor is then below triggering level, and it commences to charge via R3 once more. There is, in consequence, a 1 RADIO & ELECTRONICS CONSTRUCTOR 686 www.americanradiohistory.com FA/LURE MONITOR This little unit gives audible warning of mains supply cessation. D2 1N4002 +14 DI IN4002 +14 RI R3 22kn TRI BC107 CI R4 2.7kn 470n TR2 2N2646 T INF Ti B2 C3 â 5,000 BI R2 4-7kn C2 INF 6.3V NF IOVwkg : AC. mains L51 15n BI 822 B 1k07 Lead -outs 2N2646 Lead -outs The circuit of the mains failure monitor unit. The unijunction transistor oscillates at an audio frequency when the mains supply ceases train of current pulses in the speaker. With the component values shown the pulses have a repetition frequency of around 350Hz, and they result in a tone at this frequency being reproduced by the speaker. UNIJUNCTION SUPPLY The unijunction transistor supply is obtained from the Ti, the primary of which connects to the a.c. supply to be monitored. The secondary voltage is rectified by Dl and applied to the reservoir capacitor C3. C3 is also the high value capacitor which supplies the unijunction oscillator when the mains supply ceases. If TR is now taken into consideration, it will be found that the unijunction oscillator does not in prac6.3 volt secondary of transformer 1 JUNE tice operate when the mains supply is present. A second rectifier, D2, causes a rectified positive voltage to appear on the upper plate of Cl. This voltage is coupled via R1 to the base of TR1, which is thus turned hard on. Its collector holds the upper plate of C2 at a voltage slightly higher than that on the lower negative supply rail, whereupon C2 cannot charge via R3. In consequence, TRI prevents the oscillator from operating when the mains supply is on. If the mains supply ceases, the voltage across T1 secondary drops to zero. CI discharges very quickly into R1 and R2, with the result that TRI turns off. C2 is now able to charge via R3, and the unijunction oscillator commences to operate, producing an audible tone from the speaker. The oscillator obtains its power from the charged capacitor C3, and the tone continues until C3 is discharged. Thus, the unit gives audible warning of the cessation of the mains supply. If the supply is re -applied, capacitors Cl and C3 will become fully charged again and the unit will be ready for use once more. In the author's circuit, CI and C2 were plastic foil capacitors. Electrolytic capacitors of the same value and with a working voltage of 10 volts or more could alternatively be employed. The speaker gives a reasonably loud tone which should be adequate for normally quiet premises. The volume of the tone will be increased if the speaker is mounted on a small baffle or is housed in a cabinet. The speaker should have an impedance of 1552. Transformer T1 can be any heater transformer having a 6.3 volt secondary. The length of time during which the tone sounds depends on the value of C3. Where this is 5,000µF, as shown, the tone is reproduced at a high level for 15 seconds and then gradually fades out over the following 30 seconds. If desired, C3 can be given a higher value than 5,000µF. If it is made 10,000µF the tone will sound for approximately twice as long, and the time will be lengthened again if the value of C3 is increased further. Readers who have access to stocks of high value electrolytic capacitors may connect these in parallel to produce a very high capacitance for C3, whereupon the tone may be made to sound, on cessation of the mains supply, for a considerable period. If the capacitance is made very large, however, it would be advisable to insert a 1052 resistor rated at 3 watts or more between D1 and the secondary of the transformer. This resistor will reduce switch -on current surges. 1975 687 www.americanradiohistory.com FOR DX LISTENERS By Frank A. Baldwin Frequencies = kHz Times= GMT Clandestine transmissions still claim a certain amount of attention from many short wave listeners. As a change from logging some of the fairly regular "bread and butter" transmissions, chasing the clandestines can be interesting and the successful reception of some of them represents a Dx feat in itself. The aerial system must be good, the receiver in tip-top condition and the operator fully aware of the difficulties to be encountered - chasing clandestines is not noted as being an easy occupation. As an illustration of this, try the relatively easy Azad Kashmir currently (at the time of writing) operating on 3383; listen from around 1815 till signoff (usually from 1820 to 1830 after an interminably The battle here will not only be long choral the standard one of prevailing conditions but also the sea of surrounding commercial QRM. Higher up the spectrum we have the Voice of the Thai People, last logged by us in late March at 1542 on the regular 9422.5 channel, this one tending to close down around 1615 after some military music and slogans in Thai. The "Voice of the Malayan Revolution" broadcasts in English to Singapore and Malaysia from 0930 to 1000 and from 1500 to 1530 on 11830 and 15790; despite several attempts, we have singularly failed to log this one.. Radio Pathet Lao is well worth logging, listen around 6212 (frequency is apt to vary) from 1530 onwards until they sign-off at 1600 or, if you want to make life even more difficult for yourself, listen for the much weaker parallel channel on 6199, this will certainly test the sensitivity and selectivity of your receiver - not to mention the operator. CURRENT SCHEDULES THAILAND Radio Thailand, Bangkok, has an Overseas Service in English for Europe and Asia from 1040 to 1140 on 9655 and on 11905 (also on 7115 from 11.30). In the North American Service, Radio Thailand broadcasts in English from 0415 to 0530 on 9655 and on 11905. SRI LANKA The Sri Lanka Broadcasting Corporation, Colombo, directs a service in English to Europe from 1900 to 2000 on 9720, 11800 and on 15120, the newscast is from 1915 to 1920. Other broadcasts in English are from 1030 to 1130 to S.E. Asia, Japan and Australia on 11835, 15120 and on 17830;`from 0030 to 0430 on 6075-, 11725 and on 15425, from 1230 to 1730 on 7190, 11725 and on 15425 in the All Asia Service. ANGOLA The Angolan, Home Services (First Programme) radiated by Emissor Official, Luanda, in Portuguese, are as follows - from 1700 to 2400 (Saturdays to 0200) on 3375; from 0500 to 0815 (Sundays from 0600) and from 1600 to 2310 on 4820; from 1700 to 2400 (Saturdays to 0200) on 5960; from 0500 to 2400 Mondays to Fridays (0500 to 0200 Saturdays, 0600 to 2400 Sundays) on 7245; on 9535; from 0800 to 1600 on 11875. The programme is networked by Cabinda City, Cabinda on 4925; Sao Salvador, Zaire, on 4825; Henrique de Carvalho, Lunda, on 4860; Serpa Pinto, Cuando-Cubango, on 4780; Luso, Moxico, on 4970 and by Tezeira de Sousa, Moxico, on 4885. The Second Programme operates continuously on 6175 and on 7265, also on 9660 but operational times unknown. The political programme "Fighting Angola" presented by the MPLA from Nova Lisboa is radiated in the First Programme of Radio Clube de Huambo from 1720 to 1750 on 7160 and on the Second Programme from the same station from 1950 to 2020 on 5060. Programmes in English may be heard from 1130 to 1145 on 9535 and 11875 and from 1500 to 1530 Mondays to Saturday inclusive. KUWAIT Broadcasts in English from Radio Kuwait are being heard from 1700 to 2000 beamed to Europe on 11940 and to East and S.E. Asia on 9555. SPANISH SAHARA Radio Sahara, Al-Uyun, operates in Arabic from 0900 to 1330 and from 1500 to 2300; in Spanish from 0800 to 0900, from 1330 to 1500 and from 2300 to 2400 on 11805 from 0800 to 1800 and on 6095 from 1800 to 2400. - ITALY "RAI Italian Radio and Television", Rome, operate an External Service in English to the U.K. from 1935 to 1955 on 6050, 7275 and on 9710. Further RADIO & ELECTRONICS CONSTRUCTOR 688 www.americanradiohistory.com transmissions in English are - to the Near East from 2025 to 2045 on 6050, 7235 and on 9575 and to the Far East from 2200 to 2225 on 5990, 9710 and on 11905. A relay of the Home Service to the Mediterranean Basin with newscasts in German and French on the half-hours and in Italian and English on the hours is made from 2230 to 0500 on 6060. CHINA Radio Peking has the following schedules for the main domestic First and Second Programmes in Standard Chinese - First Programme from 1303 to 1730 and from 2000 to 2200 on 3220; from 0903 to 1735 and from 2000 to 2400 on 4460; from 1353 to 1735 and from 2000 to 2300 on 4905; from 0948 to 1735 and from 2000 to 0100 on 5320; from 1233 to 1735 and from 2000 to 2320 on 7935; from 2000 to 1735 on 9080; from 2203 to 1300 on 11330; from 2300 to 0800 on 12120; from 2303 to 1230 on 15030; from 0003 to 0900 on 15230; from 2304 to 1350 on 15550 and from 0103 to 09045 on 17605. The Second Programme from 1303 to 1645 and from 2100 to 2245 on 3290; from 1118 to 1645 and from 2100 to 2330 on 4250; from 1003 (0950 Weds and Fri) to 1645 and from 2100 to 0245 on 5075; from 1023 (0950 Weds and Fri) to 1645 and from 2100 to 2400 on 6345; from 2333 to 1115 on 7190; from 2248 to 1300 on 10260; from 0003 to 1020 on 11040; from 0248 to 1000 on 15450 and from 0500 to 0800 and from 2300 to 0355 on 15590. AROUND THE DIAL IRAQ Baghdad at 1945 on 9745 with identification and programme in English, news, music and talks. AUSTRIA Vienna at 1230 on 11970 with identification at commencement of the English programme. JAPAN Tokyo at 0800 on 15430 with English announcements and identification in the European Service. ROUMANIA Bucharest at 2115 on 5990 with programme in English directed to the U.K. JORDAN Radio Amman may be heard at 1700 on 9560 at which time we logged a newscast in English after station identification. CHINA Radio Peking on 11600 at 0945 with English read by a female announcer. VENEZUELA Radio Popular at 2305.on 4810 with programme of local music, many commercials and identification at 2312. This station has a schedule from 1000 to 0400 and is one of the myriad Venezuelans that can be heard on the 60 metre band. Radio Monogas at 0221 on 3325, Latin American music, commercials in Spanish, songs etc in usual LA format. PAKISTAN Islamabad at 1533 on 4835, local music and songs, OM announcer, signal just audible through noise level. NEPAL Radio Nepal at 1605 on 5007 and also in parallel on 3425, songs, local music with YL announcer in Nepali. INDIA AIR Gahauti at 1658 on 3375, OM with announcements in vernaculars then station suddenly off the air, without National Anthem. AUSTRALIA ABC Brisbane at 0804 on 4920, OM with news and announcements in English then into dance music records programme. CAPE VERDE IS. Radio Clube de Cabo Verde at 2016 on 3886 measured (listed 3883), OM announcer in Portuguese, songs and music of Portugal. GHANA Ejura at 1840 on 3350, OM announcer in vernacular, African orchestra and music, YL with song. MALAWI Blantyre at 2025 on 3380, local music, songs and chants in typical African style. AFGHANISTAN Kabul at 1710 on 4775 with a talk by male announcer until 1713 then into programme of local music. MOZAMBIQUE Radio Clube de Mozambique at 2020 on 4855, OM in Portuguese with announcements then into programme of `pops'. BRAZIL Radio Relogio at 2310 on 4905, second pulses in time -checks, OM in Portuguese, Latin American music. in Radio Brazil Central at 2330 on 4995, OM with identification then Portuguese 'pop' music programme. Radio Mexico announcing as "Radio Fiesta" (formerly announcing as "Radio Tricolour") at 2107 on 15110, typical Mexican music, Spanish announcements with frequent soundings of a siren - all heady stuff! Lagos at 2200 on 4990, OM with newscast in English after station identification. a newscast MEXICO COSTA RICA Radio Capital as late as 0810 on the regular 4832 channel with identification at 0811 after programme of local music and songs. 1 NIGERIA TOGO, Lome at 1930 on 5047 with newscast in English by male announcer, into French at 1938. SINGAPORE Radio Singapore at 1554 on 5010, light music, announcements and songs in English. UNE 1975 689 www.americanradiohistory.com your worksb i WE n CERTAINLY," REMARKED DICK chattily, "see plenty of variety in this servicing racket." He popped the last of his lunch-time sandwich into his mouth and fastidiously brushed the crumbs off the front of his overall jacket. "And what," asked Smithy. as he carefully removed the wrapping from a pork pie, "prompted that remark?" "I've just had two jobs in a row," explained Dick, "which pretty well represent the ultimate extremes in domestic electronics these days." "In what way?" By now, Smithy had exposed the crust of the pork pie. He took a large bite from it. "Well," said Dick, "both jobs were record players. One was a cheap old mono player with a single UL84 pentode amplifier and a UY85 half wave mains rectifier, and the other was a modern stereo player which had hardly anything in it except an integrated circuit for each channel. There must be nearly twenty years of design development between those two players." OPERATIONAL AMPLIFIERS "I see what you mean about variety," stated Smithy in muffled tones. "Working on valves one minute and i.c's the next certainly represents a big change." He swallowed the piece of pork pie he had been chewing, then took another gigantic bite. "Dash it all, Smithy," complained Dick testily. "Can't you bring in sandwiches for lunch like any normal person? When you have lunch the place gets to feel like a buffet on B. Railways." "But I don't like sandwiches." replied Smithy with difficulty as he struggled with the pie. "I prefer to have a bit of diversity in what I eat." As he spoke, a large piece of crust escaped. Deftly, he caught it as it fell mouth. and replaced "Ye gods," snorted Dick in a tone of utter revulsion. "Watching you eat is enough to put anyone off food for the rest of his life. I've forgotten what I was talking about now." "You were talking about valves," said Smithy helpfully, "and integrated circuits." "Oh yes, that's right. Well, I'm getting quite used to integrated circuits now but there's one thing about them I don't understand." "What's that?" "You often read about integrated circuits being used as operational amplifiers. But the integrated circuits I bump into in the sets I service are a.f. or i.f. amplifiers and things like that. I don't recall even seeing any i.c. that could be called an operational amplifier. Come to think of it, I'm not all that certain what an operational amplifier is!" Smithy, his mouth temporarily clear of pork pie, was able to give an audible chuckle. "Many of the amplifying integrated circuits you see in sets," he remarked, "are in fact loosely based on operational amplifier principles, with the design directed towards a particular end such as driving a loudspeaker. But so far as straightforward operational amplifiers are concerned, you won't find any of these in a conventional domestic set." "All right then," said Dick. "If that's the case, what are operational amplifiers intended for?" This month Smithy the Serviceman, accompanied as always by his able assistant Dick, embarks on a consideration of operational amplifiers in general and the 709 in particular. He will be concluding on the subject of op -amps next month. "Initially," said Smithy, "operation- al amplifiers were meant to be used in analogue computers. An operational amplifier is a device having an extremely high level of voltage gain. By coupling a suitable negative feedback circuit to it the amplifier gain is reduced, and it then carries out a function which is controlled by the feedback circuit. For instance, a simple resistive feedback circuit can cause an operational amplifier to have a voltage gain which is entirely controlled by the values of the resistors. If the feedback circuit is capacitive the amplifier becomes capable of changing a square wave to a triangular wave of the same frequency. There are all manner of feedback circuits which can cause an operational amplifier to carry out different functions. You can even have a negative feedback circuit where the output connects directly back to the input. The amplifier then has a gain of unity and can be employed as a voltage follower." "Blimey," said Dick, impressed. "These operational amplifiers seem to be pretty versatile." "In combination with the feedback circuits they are," stated Smithy. "Apart from computer work op -amps, to give them their shortened name, lend themselves to no end of applications in test equipment and things like that, and they are very interesting gadgets for the home constructor to play around with. They are, of course, readily available from many component suppliers, and what are probably the most popular types are the 709 and the 741. The 709 is rather a venerable device these days, since it first came on the scene about ten years ago. The 741 is a more recent version and is in many ways an improvement RADIO & ELECTRONICS CONSTRUCTOR 690 www.americanradiohistory.com on the 709. You'll usually find these two op -amps referred to with a letter after the three figures, such as 709C or 741C. There may also be some letters and numbers before the three figures. For instance, the full Texas instruments names for the two devices are SN72709 and SN72741 with a letter following to indicate the type of package." "Type of package?" "The size and shape of the device and the number of pins it has." C') DIFFERENTIAL AMPLIFIERS "Oh," remarked Dick. He absorbed this information whilst Smithy continued to eat his pork pie. "If," remarked Dick thoughtfully, "an op -amp can have negative feedback from its output back to its input, then the input must be out of phase with the output." Smithy put his pie on one side for a moment. "True enough," he agreed. "But that doesn't give the full picture. An op amp has one output and two inputs. One input is known as the inverting input and it is out of phase with the output. That's the input to which negative feedback is applied. The other input is referred to as the non inverting input and it is in phase with the output. In circuit diagrams the inverting input is marked with a minus sign and the none -inverting input is marked with a plus sign. The two op amp inputs go to the bases of two transistors in a differential amplifier." "Blow me," said Dick bleakly. "This op -amp business is getting complicated already, and we're only at the input stage! What in heck is a differential amplifier?" "It's simply another name for what you may know as a long-tailed pair. Here, I'll show you." Smithy beckoned Dick towards him, then pulled his note pad over and sketched out a circuit. (Fig. 1.) Output. Input Input 1. A differential amplifier. In this instance an output is taken from the collector of one of the transistors Fig. JUNE (a ) to - (b) If a positive -going signal is applied to the base of the second transistor in the differential amplifier, the collector of the second transistor goes negative (b). When a positive -going signal is fed to the base of the first transistor, the collector of the second transistor goes positive also Fig. 2 (a). "Now here," he continued, "is a differential amplifier. The two transistors are a matched pair and the two collector load resistors are equal in value. Let's say that we take an output from the collector of the second transistor. Now, what happens if we apply a positive-going input to the base of this second transistor?" (Fig. 2(a).) "Why," said Dick, "its collector will go negative. The collector will go in the opposite direction to the base." "Fair enough," commended Smithy. "Now what happens at the output if we apply a positive-going input to the base of the first transistor?" (Fig. 2(b).) "Ah," said Dick thoughtfully, "there are a few more steps involved here. Now if the base of the first transistor goes positive the emitter, due to the emitter follower action, will also go positive. This means that the emitter of the second transistor goes positive, too. The emitter of the second tran- 1975 sistor going positive has the same effect as the base of the second transistor going negative, and so the collector of the second transistor goes positive." "Very good," stated Smithy approvingly. "To sum up, the output from our differential amplifier goes negative if the base of the second transistor goes positive and the output goes positive if the base of the first transistor goes positive." "That seems to be about it." "Right," said Smithy briskly. "Now, I'm going to redraw that differential amplifier and introduce an earth or ground point into the circuit. This earth is a central point and will be common with the chassis of the equipment on which the differential amplifier would be fitted. We will now have an upper supply rail which is positive of earth and to which the two collector resistors connect. And we will also have a lower supply rail of the same voltage, but which is negative of 691 www.americanradiohistory.com oV oV Constant current generator (a) (b) Direct coupled amplifier -b.. Direct Output OV coupled input .-Output amplifier Non -inverting OV (+)--Y Inverting input (-) Constant current generator Constant current generator (c) (d) Fig. 3(a). Here, the differential amplifier is powered by supply rails that are positive and negative of earth (b). Differential amplifier performance is improved if the common emitter resistor is replaced by a constant current generator (c). A direct coupled amplifier is added after the differential amplifier (d). The whole system is now an operational amplifier with inverting and non -inverting inputs earth. '1 he common emitter load will be connected to this lower negative rail. Okay up to now?" (Fig. 3(a).) "Yes," said Dick, looking at the new circuit Smithy had sketched out. "In other words, the earth point is mid -way between the positive and negative supply rails." "That's right," said Smithy. "I'm next going to take the simple step of replacing the common emitter resistor with a constant current generator. This can consist of a single transitor with its base held at a fixed potential and with a suitable value of resistance in its emitter circuit. A constant current generator has the same effect as a very high value common emitter resistor and it ensures that the two differential amplifier transistors share a fixed current." (Fig. 3(b).) "All right" said Dick, frowning. "I'm still with you." "Good," stated Smithy, busy yet again with his pen. "I'm next going to connect the output of the differential amplifier to a rather complicated direct coupled transistor amplifier which I'll represent as a block. This direct coupled transistor amplifier does three things. First, it provides more voltage amplification. Second, it has a totem pole output stage roughly similar to the Class B audio output stage you get in transistor radios, and this gives a low impedance output voltage with plenty of current drive behind it. And third, the direct coupled transistor amplifier shifts the standing voltage level of the signal at the collector of the second transistor in the differential amplifier such that, when both the differential amplifier bases are at earth potential, so also is the output from the direct coupled transistor amplifier." (Fig. 3(c).) "Phew," gasped Dick, "that's a fair old work load for one amplifier, isn't it?" "It is rather," conceded Smithy. 692 "Still, it's marvellous what you can do with transistors if you connect enough of them up in the right way. Now, there's a further point about the direct coupled amplifier which I next need to introduce, and this is that its output is in phase with the input it takes from the differential amplifier. If the collector of the second transistor in the differential amplifier goes positive so also, by an amplified amount, does the output of the direct coupled amplifier. The same thing happens in the negative direction. Can you see what we now have?" "No, what do we have?" "We have a card -holding fully paid up duly certified operational amplifier!" OP -AMP INPUTS Whilst Dick gaped at Smithy's circuit in the light of this intelligence, the Serviceman picked up his pork pie RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com and took another enormous bite. "These darned pies," he grumbled, "never seem to have any taste in them these days." "Perhaps," said Dick absently, "it needs a bit of mustard." "That," remarked Smithy, "is what I call good thinking." Leaning forward, he picked up a small Philips screwdriver and, with its aid, bored four deep holes into the meat of the pie. Opening a drawer in his bench he produced a tube of Colman's mustard, the cap of which he removed. He next applied the end of the tube to each of the four holes, filling each with mustard, after which he replaced the cap on the tube. He took a further bite of the mustardlaced pie. "Ah," he muttered contentedly, "that's a bit more like it." But Dick had eyes only for the sketch on Smithy's note pad. "Tell me more about this amplifier circuit, Smithy." "Okey-doke," replied Smithy obligingly. "Now, the overall amplifier has two inputs. Following from what we've seen up to now, if the input at the base of the second transistor in the differential amplifier goes positive the final amplified output goes negative. So the input to the base of the second transistor in the differential amplifier is the inverting input of the op -amp and we can identify it with a minus sign. At the same time, if the input to the base of the first transistor in the differential amplifier goes positive so also, in an amplified manner, does the final output of the op -amp. So this is the non -inverting input of the op -amp and we can mark it with a plus sign." (Fig. 3(d).) "Why," asked Dick, "do you have to have a differential amplifier? Couldn't the op -amp just consist of a simple straight -through amplifier with single stages following each other in sequence?" "The first reason for using a differential amplifier," replied Smithy, "is that it enables you to have balanced inverting and non -inverting inputs. When there is a constant current generator in the common emitter circuit the inputs both have the same sensitivity, so that an input of a small fraction of a volt at the non -inverting input causes the same voltage change at the op -amp output as does an input of the same fraction of a volt at the inverting input. Another good reason for having a differential amplifier is that the two halves stabilize each other. In consequence, any changes in performance due to temperature or supply voltage variations in one transistor are balanced out by similar changes in the other. This balancing out process will be particularly effective when the two transistors are on a single chip in an integrated circuit. Now, there is a third advantage given by the differential amplifier which introduces another new point about the op -amp." JUNE "Fire away!" "I said just now," remarked Smithy, "that the output of the op -amp is at earth potential when the two inputs are both at earth potential. Now, the output of the op -amp will also be at earth potential when both the inputs have the same potential even when this potential is quite some way positive or negative of the earth point. This facility can be quite useful for a lot of op -amp applications." "Gosh, that's another thing I've learned," exclaimed Dick. "Wait a minute, though! There's something that's worrying me here." "What's that?" "You say that the direct coupled transistor amplifier following the differential amplifier causes the voltage level to be shifted so that the op -amp output is at earth potential when the two inputs are at the same potential. Now, I'm prepared to believe that an op -amp has many magical qualities but I cannot for the life of me accept that you can have a transistor circuit which works as precisely as that." "Your scepticism," pronounced Smithy, "does you credit." "Does it?" said Dick happily. "I knew I couldn't be wholly bad." "And I say that," continued Smithy, "because in practice the direct coupled transistor amplifier cannot take the output exactly to earth potential when both inputs are at the same potential. Instead, it tends to take the output towards earth potential. To get the output exactly at earth potential one or other of the two inputs has to be made very slightly positive of the other. The voltage involved is quite small and it varies with different op -amps. It is referred to as the `input offset voltage'. There is another allied term here, this being `input offset current'. This is the difference between the currents flowing into the inputs when the op -amp output is at earth potential. Again, it is quite a tiny figure." 709 OP -AMP Smithy rose, walked over to the filing cabinet, and returned with a bulky manufacturer's data book on linear integrated circuits. He leafed through the contents, then opened out the book at a page on which appeared a circuit diagram. He laid the book down on his bench and indicated the circuit to his assistant. (Fig. 4.) "Now here," he remarked, "is, the internal circuitry of an actual op -amp. It is, in fact, what you get inside a 709 operational amplifier." "Hell's teeth," stuttered Dick. "There are enough transistors here to start a mail-order business." "Actually," said Smithy soothingly, "there are only fifteen transistors on the chip. Don't forget that we are now entering the Realm of the Integrated Circuit, where it's usually easier to add a transistor than a resistor, and where inductance is absent and capacitance is Your Local Supplier LONDON THE MODERN BOOK CO. Largest selection of English & American radio and technical books in the country. PRAED STREET, LONDON, W2 1NP 19-21 Tel: 01-723 4185/2926 ST. HELEN'S RADIO Hi-Fi Equipment Tape Recorders Radio Receivers Television SPECIALISTS IN RADIO & ELECTRONIC TEXTBOOKS ST. HELENS GARDENS LONDON, W.10 Tel: 01-969 3657 HAMPSHIRE BOURNEMOUTH LARGEST HI-FI AND RADIO COMPONENT STORE IN THE SOUTH FORRESTERS NATIONAL RADIO SUPPLIES LTD. 70-72 Holdenhurst Road Bournemouth Icicpliouc 25232 SURREY WITWO RTH TRANSFORMERS TV Line out -put transformers Manufacturers of the largest range in the country. All makes supplied. Modern BAIRD, BUSH, GEC, PHILIPS Replacement types ex -stock. For "By -return" service, contact London 01-948 3702 Tidnfan Mail Order Ltd., Dept. R.C. 236 Sandycombe Road, Richmond, Surrey TW9 2E0. Callers welcome. 693 1975 www.americanradiohistory.com Internal frequency compensation o JA +supply 20kn IOkn Output transistor 25kn 25kn Darlington pair 3kn o Inverting input Differential amplifier 36kn (-) o Constant current generator Non-inverting input Output (+) 18kn Output driver Output frequency compensation Output transistor 10kn 24kn o -supply Fig. 4. The internal circuitry of the 709 op -amp, with some of the transistor functions identified very hard to come by. Despite the fact that there are more transistors here that you'd employ in a similar sort of circuit using discrete devices, it's still fairly easy to find a few familiar configurations." "If," remarked Dick despairingly, "you can see anything familiar in that jungle then you must have e.s.p. or something." "For a start," said Smithy, ignoring his assistant's comments, "take a look at the inverting and non -inverting inputs. These go straight to the bases of two transistors which form a differential amplifier just like the one we've been discussing up to now. Also, there is a single transistor in the common emitter circuit which acts as a constant current generator exactly in the manner I described just now." "Why," stated Dick excitedly, "I can see that now! Also, there are two 25k12 resistors in the collector circuits of those differential amplifier transistors. Together," he ended disconsolately as his elation faded, "with a whole conglomeration of other transistors." "Well," said Smithy, "if you look closely you'll see that two of those transistors form a Darlington pair which couples the collector of the second differential amplifier transistor to the voltage shifter and output driver circuit. You can see the same pattern of transistors and resistors in the. collector circuit of the first differential amplifier transistor. These two sets of transistors keep the differential amplifier collector circuits balanced out and symmetrical, and they stabilize the differential amplifier against changes in temperature and supply voltage. The three transistors which follow the Darlington pair couple through to the two output transistors. These have their bases connected together and act as output emitter followers in much the same way as two emitter follower output transistors in an a.f. amplifier. The transistors which precede them ensure that the output voltage is at earth potential when the inverting and non -inverting inputs are at the same potential. Or, rather, when the inverting and non -inverting inputs are at potentials which are within the offset voltage range." "Those two output transistor bases," a said Dick critically, "are connected together directly. In an audio output stage, though, you'd have a diode or a resistor or something like that between the two bases to keep the transistors turned partly on in the absence of signal. Won't you get crossover distortion with the output circuit you've got here?" "You will," agreed Smithy. "However, the op -amp will normally be used with a high level of negative feedback and this will effectively reduce the distortion to a very low level." "There's another thing I've just spotted," said Dick thoughtfully. "The base and collector of the first transistor in the Darlington pair are taken out to two pins marked 'Internal Frequency Compensation'. Also, there's another pin marked, `Output Frequency Compensation'. What's all this compensation business, Smithy?" "The word `compensation'," grinned Smithy, "is a euphemistic term for a process which ensures that the i.c. doesn't take off at a high frequency! RADIO & ELECTRONICS CONSTRUCTOR 694 www.americanradiohistory.com 500pF I S base of the transistor which drives them. Again, you have quite obvious high frequency attenuation." "I wonder why they call them `compensation' circuits." "Well," said Smithy, "the word `compensation' is frequently used when you have a component which alters frequency response in a circuit. For instance, TV video peaking chokes are also referred to as `compensating krt A B Internal frequency compensation Output 2OpF o Output frequency compensation Fig. 5. External frequency compensating circuits are connected to the appropriate op -amp pins as illustrated here. The capacitor values shown are representative There's stacks of gain on the i.c. chip and if you just connected a supply up to it and did nothing else it would simply burst into high frequency oscillation. To prevent this, external capacitance is coupled to the frequency compensation points to hold down the high frequency response. Like this." Smithy added external frequency compensating components to the circuit of the operational amplifier. (Fig. 5.) "As you can see," he went on, "one of the frequency compensating external circuits consist of a series resistor and capacitor coupling the collector of the first Darlington pair transistor back to its base. Such a circuit obviously introduces high frequency attenuation at this point in the amplifier chain. The output compensation is provided by a single capacitor which couples from the output transistor emitters to the chokes'." Pleased with his excursion into the field of etymology, Smithy picked up the remainder of his pork pie and took a further massive bite. A thin stream of mustard shot out and splattered over the circuit of the 709. Dick turned round and, unbelievingly, looked at the Serviceman. A competent cosmetician would have unhesitatingly declared that, whilst the layer of yellow on Smithy's lips might well be quite striking, it was otherwise most unbecoming. "Look," said Dick flatly. "I'll go out now and I'll come back in again in two minutes' time. By then you should have consumed the very last piece of that revolting pork pie of yours." "You needn't bother," replied Smithy airily, albeit indistinctly. "The final bit is going in right now." Shuddering, Dick waited whilst Smithy masticated his way through the ultimate remnants of pie. The Serviceman then drew out a large handkerchief and, with a flourish, wiped his lips. "Thank goodness for that," said Dick in a relieved tone, "now let's get on with a bit more gen about this 709. What about the pin connections, for instance?" "You can see them in this data book," said Smithy. "Here you are." He pointed to three pin layout diagrams on the page in front of them. (Fig. 6.) Int. freq. comp. Supply Inv. input - Int.freq. Int. freq. I Inv. input C 2 Non-inv. input C 3 Supply- C 4 7 comp.A 7 7 Supply + 6 7 Output I 14 N.C. N.C. 2 13 N.C. 3 12 Int. freq. comp. A input 4 II Supply Non-inv. input 5 IO Output Inv. 7 Out. freq. comp. N.C. Int. freq. comp. B 8 5 E. JEFFRIES For your new television set tape recorder, :transistor radio and hi-fi equipment PHILIPS, ULTRA, INVICTA DANSETTE, MASTERADIO, PERDIO, MARCONI, PHILCO FIDELITY 6A Albert Parade Victoria Drive, EASTBOURNE SUSSEX EIRE FEATS for PARTS ELECTRONIC COMPONENTS RADIO & TELEVISION For the convenience of Irish enthusiasts we supply Radio & Electronics Constructor Data Books and Panel Signs Transfers Also a postal service Wm. B. PEAT & `Co. Ltd. 28 PARNELL STREET DUBLIN 1 Greenbank Electronics FREE! Data and circuit diagram for Digital Clock Chip AY -5-1224, Digital Alarm Clock Chip, MK 50253, also data sheet for Economy DL -747, DL -750 LEE) displays. (A stamped addressed envelope with enquiries would be a great help to us, but is not essential). reset, easy display interface, 16 pin package. £3.66 MK 50253, 4/6 digit alarm clock chip, 50 Hz, 12/24 hr., AM/PM Et activity indication, 'snooze' feature, Out. freq. comp. Supply SUSSEX CLOCK CHIPS (ADD 8% VAT) AY -5-1224, 4 digit, 12/24 hr., 50/60 Hz, TTL compatible, zero Output Non-inv. input comp. B C -I- Four Local Supplier Supply - N.C. -1- Out. freq. comp. N.C. intensity control, simple time setting, 28 pin package. £5.50 L.E.D. DISPLAYS (ADD 25% VAT) DL -747 15mm (0.6") high, common anode £2.04 DL -750 15mm (0.6") high, common cathode £2.25 Add VAT at the appropriate rate to all prices, post etc. 10p + VAT per order. 709 OP -AMP TOP VIEW Fig. 6. Pin connections for the 709 in its three most common packages JUNE 1975 GREENBANK ELECTRONICS (Dept. C6R), 94 New Chester Road, New Ferry, Wirral, Merseyside. L62 5AG. Tel: 051-645 3391 695 www.americanradiohistory.com "There are three generally available versions of the 709," he went on. "One is in the round TO99 can, which is about the same size as a TO5 can, and the other two are in 8 pin dual-in -line and 14 pin dual-in -line. You'll note that the round can and 8 pin dual -inline packages both have the same lead out numbering. The 14 pin d.i.l. package is really the same as the 8 pin d.i.l. package with four 'no connection' pins added at one end and two 'no connection' pins added at the other. The letters d.i.l. are, of course, short for `dual -in-line'. Sometimes, you'll see the abbreviation d.i.p. instead." "What does that mean?" "It means dual -in-line together with with fact that the chip is in a plastic Radio Topics encapsulation." AFTERS "Fair enough?' remarked Dick. "What about performance figures?" "You can," said Smithy, "get the more important ones from this data book." Smithy pointed out the principal parameters for the 709 i.c. to his assistant. Dick studied these carefully. 709 - Principal Parameters Supply voltage (VS+ and VS-) 18V max. Supply current (VS -15V) 2.6mA typical Input voltage range, either input ±10V 2000 Minimum output load Input offset voltage 2mV typical Maximum p -p output swing , 28V typical Large signal voltage gain 45,000 typical 250kO typical Input resistance Total dissipation (below 70°C 300mW max. ambient) "Blimey," he remarked, "the typical voltage gain is no less than 45,000 times." "True," agreed Smithy. "That's before you add the negative feedback, of course." "You were saying," went on Dick, "that the 741 op -amp is an improvement on the 709. How about giving me the low-down on the 741 ?" "I'm afraid," said Smithy regretfully, "that we've come to an end so far as this particular gen -session is concerned. I'll deal with the 741 when we have our next technical natter, and I'll also show you how you can use op amps in, simple circuits which do not require separate positive and negative supply rails." Whereupon Smithy, having brought the discussion to an end, reached to the back of his bench and produced a McVitie's Bramley Apple Pie for further sustenance. And what, dear reader, can be more fitting than applie pie to terminate an interlude which takes in pork pie for bodily nourishment and the 709 op-amp for mental stimulation? By Recorder WE WOULDN'T HALF BE IN TROUBLE if all the electrons went on strike.' So spoke a junior member of the Recorder family this last winter as we sat in front of a nice warm electric fire watching a TV programme relayed by satellite from America. He was right, too. NO ELECTRONS Just imagine what would happen if, for some reason, electrons decided that they would no longer travel through conductors in the obliging manner that they do at the present time. We would at gnce be returned to the days before electricity when the only source of mobile power was steam and human effort. There would be no radio, no television, no telephone, no electric light or heat, no cars and no services where electricity plays any part in their functioning. Admittedly, our forebears coped quite happily with a world of this type, but that was mainly because they had nothing better to compare it with. Also, there were a lot less of them then than there are of us now, and the human way of life had not in those days assumed the crowded, complicated and interdependent state at which it has currently arrived. If we were unexpectedly robbed of electricity virtually all our mass-production food plants would come shuddering to a halt, and it would not be long before our civilization, precarious enough as it is, just finally gave up all pretence of adequacy and slowly crumbled away. None of us have ever seen any electrons but we all take it for granted that they exist and that, when set in motion, they do all sorts of useful things such as producing heat and creating magnetic fields. Could it be that electrons actually do not exist? Could it be that it is only our faith in 696 electrons that enables us to do tricks with conductors and insulators which are only an order or so of complexity ahead of the remote bending of forks? Suppose a TV cameraman suddenly asked himself why on earth he was pointing a metal box with a pattern of knobs on the outside towards an artiste; suppose he decided to himself that the processes carried out by the camera were so improbable that they just could not happen; suppose he considered that it was entirely unfeasible that a jumble of invisible electrons could flow in planned directions and, as a result, send as evanescent a thing as a picture down a length of wire. Would his lack of credence cause the signal from his camera to gradually fade away to nothing? And if this refusal to accept the presence of the unperceivable electron were to spread to other members of the studio crew could not.. . Hallo, my desk lamp has just started flickering. Okay, Electron, I take it all back. I believe! You exist, you are, and you flow for ever on your preordained quest towards the everlasting Positive. FIGURE FACTS Quite a few fortuitous things happen in electronics and general physics, and a striking example of this is the fact that the velocity of light happens to 6e 299,776,000 metres per second. if we take this to 3 significant figures we can, then work, for general applications, to the very convenient figure of 300 million metres per second as the velocity of light and, of course, of radio waves. Some reference books quote slightly different figures for light velocity incidentally, so please don't write in and say I've got it wrong. For instance, Langford -Smith's `Radio Designer's Hanbook' Fourth Edition (Iliffe) gives the velocity as 299,790,000 RADIO & ELECTRONICS CONSTRUCTOR www.americanradiohistory.com metres per second. I took the figure I mentioned from 'A Dictionary of Electronics' by S. Handel, published as a Penguin paperback. Since radio wavelength in metres multiplied by frequency in Hz can be considered to come to 300 million, we can say that 3MHz corresponds to a wavelength of 100 metres, 30MHz to 10 metres, 300MHz to metre, and so on. When, in the earlier days of radio, the frequency ranges were being sorted out, it was decided to work in terms of wavelengths to powers of 10. In consequence, the range below 30kHz (or 10,000 metres) was designated very low frequency (v.l.f.), 30 to 300kHz as low frequency (1.f.), 300 to 3,000kHz as medium frequency (m.f.), 3MHz to 30MHz as high frequency (h.f.) and 30MHz to 300MHz as very high frequency (v.h.f.). They had to dig in the dictionary as higher frequencies became usable, whereupon 300 to 3,000MHz appears as ultra high frequency (u.h.f.) and, wait for it, 3,000 to 30,000MHz comes up as super high frequency (s.h.f.). Then, when a 30,000 to 300,000MHz range had to be considered viable this was called, rather lamely, extremely high frequency (e.h.f.). In the U.K. some far-sighted genius of the past chose 200kHz, or 1,500 metres, for the B.B.C. long wave station which is now Radio 2. The 200kHz signal is picked up by a number of companies making electronic equipment, and its carrier is employed as a frequency standard having a very convenient round number value. The line output stages of many television receivers radiate a fairly strong signal at line frequency and its harmonics, with the result that if you hold a portable radio tuned to Radio 2 on 200kHz close to a working TV set you can get a background beat whistle whose volume depends on the level of the line frequency harmonic radiated by the televsion set and the strength of the Radio 2 signal in the locality. This pick-up, by the way, is normally much higher with very old radios having a wire aerial than it is with sets having a ferrite rod aerial, possibly because the wire aerial offers a higher capacitive coupling to the radiating TV set. 1 BEAT FREQUENCIES Nominal line frequency on a 405 line set which is locked to a signal is 10,125Hz, and its 20th harmonic pops up at 202.5kHz. This gives a 2.5kHz beat note with the 200kHz Radio 2 signal. Locked line frequency on 625 lines is 15,625Hz (easy to remember because the last three digits are, fortuitously again, 625), and its 13th harmonic is 203,125Hz. The beat note given with the Radio 2 signal is therefore 3.125kHz. So you have spot frequencies of 2.5 and 3.125kHz available, albeit in a roundabout manner, if you're experimenting with an audio oscillator and want some comparison tones to determine what its output J frequency is. In practice, the beat note frequency with 405 lines is of an approximate nature only, since the 405 line signal is CS2 PRACTICAL PAPERBACKS normally locked to the U.K. electricty Grid, and could fall a little if the Grid FROM frequency drops during heavy consumption periods. The 625 line signal is much better, and line frequency is THE COMPLETE held, at the transmitter, to f0.15Hz. SHORTWAVE LISTENERS Multiplied by 13, this gives 1.95Hz only as the tolerance on the 3.125kHz HANDBOOK £2.10 beat note. by Hank Bennet Piano notes offer useful comparisons ELECTRONICS £t when one is trying to determine audio PHOTOGRAPHY £1.85 frequencies. If you've had the piano by Robert M. Brown Et tuner in recently, the C two octaves Mark Olsen above Middle C should give 1,046Hz, and the B immediately below it 988Hz. GETTING THE MOST OUT A popular audio frequency for signal OF YOUR ELECTRONIC generator modulation is 400Hz and, CALCULATORS £1.85 here, the G above Middle C gives by William L. Hunter 392Hz. As with the velocity of light, some text books may give slightly INDEXED GUIDE TO different frequency figures for these MODERN ELECTRONIC notes. Whilst talking about finding CIRCUITS £1.90 audio frequency standards, I am by Robert L. Goodman indebted to G. W. Short for the information that if a pre-decimal penny MODEL SAIL AND is balanced on the little finger it will POWER BOATING... ring at about IkHz when tapped with a by remote control £1.80 screwdriver. (This fact appeared in by George Siposs G. W. Short's article `LCR Tone Control Circuit' which was published RF AND DIGITAL TEST in our May 1971 issue.) Many houses EQUIPMENT YOU CAN have pre-decimal pennies lurking away BUILD £1.95 somewhere, probably in the box where edited by Wayne Green the buttons are kept. Turning to dimensional figures, it is AMATEUR FM possible to use enamelled copper wire CONVERSION Et if you want to feel out spacings in tens CONSTRUCTION of thousandths of an inch. 34 s.w.g. PROJECTS £2.10 enamelled wire is approximately 10 by Ken Sessions, Jnr. `thou' thick, 26 s.w.g. enamelled/wire is approximately 20 `thou' thick and CAR STEREO SERVICE 22 s.w.g. enamelled wire is approxiEt INSTALLATION £1.95 mately 30 `thou' thick. The actual by Paul Dorweiler Er thicknesses within tolerances of these Harry Hansen wires are, respectively, 0.0099 to 0.0104in., 0.0193 to 0.0199in. and COLOUR TV TROUBLES 0.0296 to 0.0303in. The enamel on the (FACTBOOK) £2.30 wire should be normal oil -based, and by The Editors of Electronic this is the type usually sold by home Technician/Dealer constructor retailers. Before concluding on the subject of ELECTRONIC TEST figures, here is a final little item of EQUIPMENT and how interest. If a capacitor charges up to a to use it £1.85 voltage via a resistor, it reaches 63 by Joe Risse of the voltage after the time constant period has elapsed. Similarly, if a ELECTRONICS charged capacitor discharges into a UNRAVELLED -A new resistor the voltage across its plates commonsense falls to 37% of its initial voltage after approach £1.90 the time constant period has transby James Kyle pired. The time constant in seconds is the product of the resistance and SIMPLIFIED COMPUTER capacitance in ohms and farads or, PROGRAMMING more conveniently, in megohms and The easy RPG way £1.95 microfarads. What is perhaps of by Kelton Carson greater interest is that a capacitor charges to half the applied voltage after 0.7 times the time constant, and that it similarly discharges to half the initial voltage after 0.7 times the time constant. This can be a useful thing to FOULSHAM-TAB LTD. remember if you are designing any YEOVIL ROAD, SLOUGH, BERKS. unusual timing devices. FOULSHAM-TAB f - - UNE 1975 697 www.americanradiohistory.com DIRECT SUPPLY SERVICE TO READERS . . TOWERS INTERNATIONAL TRANSISTOR SELECTOR This is dead! Japanese. And we think that they will solve 90% of your transistor enquiries. If it takes you longer than minute to find out all about these transistors then you need a copy of TOWER'S INTERNATIONAL TRANSISTOR SELECTOR. Its one of the most useful you will o working or Ing books ch be offered this year. And X probably the cheapest m In it you will find a really international selection of 10,000 transistor types - British, Continental European, American and 1 Current and widely used obsolete types were carefully selected and arranged in Numero -Alphabetical order by an author who was uniquely qualified to do the job. With his compendium, all you need to know is the type number and you can learn all about a transistor's specification; who made it and whereto contact them ; or what to use to replace it. Would this replace it? B ! Look at the entry for 2N909 PM TRANSISTOR OA LT NUMBER 25909 NS T I PACK- LEAD INFO AGE VCB VCE VEB MAX MAX MAX 60V 30V LO1 TO18 5V TOT 200MA 175C 500MVEF V..,,R V..,Vao I, I, 5, LEAD THIN MAXMUM MAX MAX M. MAX MIN MAT 3 POT NO T, Et (EXAMPLE) MOO MS T011 LOT BOV TON 5V P,o, Co. . 1 USE BIAS MAX 110 S00 MO MA T7501AWF SOLI .25P MM SUP UK ER USA SUB SUS BEH 50 MA MSG SGT 33 IBS IN 731 MIN MAX 50M 25P EURO BIAS USE MFR MT USA FE EOVT. ISS 110MN 50MA »AG SGI BS%33 25731 0 FE H Tower's International Transistor Selector This is what you will learn from it TYPE OB T P MAX H C F J C MAX 0 by T. D. TOWERS MBE, MA, BSc, C Eng, MIERE £3.40 inc. post and packing FOOTNOTE NUMERO ALPHABETIC LISTING N P 5 EIA -ADEL IN STANDARD - MPS - PIMPS G - SUGGESTED REFER TO CASE. PROELECTRON STANDARD POSSIBLE OUTLINES C APPENDIX SUBSTITUTE DETAILS- B MAXIMUM PERMISSIBLE COLLECTOR -BASE VOLTAGE WITS EMITTER OPEN SUPPLIER Of DEVICE -SCE - COLLECTOR -EMITTER VOLTAGE WITH SASE OPENCINCUIT MAXIMUM PERMISSIBLE EMITTER -BASE VOLTAGE WITH COLLECTOR OPENCMCUII MAXIMUM PERMISSIBLE COLLECTOR CURRENT MAXIMUM PERMISSIBLE JUNCTION TEMPERATURE -"f" - IN MAXIMUM KRMISSTBLE DEVICE DISSIPATION FREE AIR AT I5'C. -C WITH CASE SURFACE MELD AT AIR AT IS'C WITH METAL MEAT 2S'C PK - IN FREE ---- - SINK ATTACHED TO DEVICE - - ----- ------ OPP. F,. INDICATED IN GIGAHERTZ R KILOHERTZ M - MEGAHERTZ G FREQUENCY AT WHICH COMMON EMITTERCURRENT GAIN DROPS TO UNITY TYPICAL f, CAN HE TAKEN A5 ROUGHLY TWICE F. ,,., (SS F CODE INDICATION OF APPLICATION USAGE SHE APPENDIX A MAXIMUM PERMISSIBLE - to the address shown below - "SUPPLIER- APPENDIX copy/copies Please send me CODE INDICATION POSSIBLE CIRCUIT MINIMUM FREQUENCY CUT 1 LTD. 57 MAIDA VALE LONDON W9 1SN POSSIBLE SUBSTITUTE GERMANIUM SILICON REFER TO LEAD To:-DATA PUBLICATIONS SUGGESTED COLUMN INDICATES ISSUE NO NAME MAS CURRENT AT WHICH CURRENT GAIN M., IS CHARACTERISED CURRENT GAIN. SOMETIMES RELATEDNOR A C ADDRESS DC (BUT GAIN) AT I,7 BIAS SPECIFIED- WHERE PCALMIN (' MN- I ONLY IS SPECIFIED TYPCAL ll'P I CAN BE TAKEN AS TWICE MIN AND VICEVERSA MAXIMUM COLLECTOR CAPACITANCE (TYPICAL USUALLY j TO j MAXI -NORMALLY EMITTER OP[N CIRCUIT AND INDICATED BY "I- N . NANOFARAO-FOR HE PICOFANAO OR DEVICES C., Is GIVEN AND PICOFARADS THEM OF P' INDICATED SY 01 DATA LINE ENTRY (Block capitals) L j RADIO & ELECTRONICS CONSTRUCTOR 698 www.americanradiohistory.com SMALL ADVERTISEMENTS BENTLEY ACOUSTIC CORPORATION Rate: 5p per word. Minimum charge 75p Box No.1 Op extra. LTD. All prices inclusive of V.A.T. The Old Pollee Station, Gloucester Read, LITTLEHAMPTON Sussex. PHONE 6743 OB2 3V4 5Ú4G Advertisements must be prepaid and all copy must be received by the 4th of the month for insertion in the following month's issue. The Publishers cannot be held liable in any way for printing errors or omissions, nor can they accept responsibility for the bona fides. of Advertisers. 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ECC401.17 ECC81 ECC82 ECC83 ECC84 ECCBS ECC88 ECC807 .88 .78 .78 3OFLI 30FL2 30FLI4 £2 30L15 30L17 .82 .76 .76 30P12 ECH35 ECH42 ECH81 ECH83 ECH84 ECL80 ECL82 ECL83 ECL86 EF22 EF40 35W4 .59 35Z4GT .82 1.00 .70 SOL6GT.76 85A2 .70 807 5763 1.17 ATP4 AZ3I DAF9I DAF96 DF91 DF96 DX91 DK92 DK96 DL92 DL96 DY87/6 DY802 .41 .47 .52 HVR2A 1.76 .59 .70 .35 .59 .35 .59 .53 .82 .70 .47 .64 EF4I EF80 EF87 EF85 EF86 EF89 EF9I EF92 EF98 EFI83 .41 EF184 .41 EH90 EL32 EL34 E88CC .88 EI8OF 1.17 EA50 .32 1.17 KTW6I 1.41 MOOT .88 50CS .40 .39 .39 ECF80 .53 ECF82 .53 ECF86 .88 ECF804 30PI9 .88 30PLI 1.00 30PLI3 1.11 30PL141.29 SOBS .76 .64 .47 .82 EY51 .47 EY83 .63 EY87/6 .39 EY88 .47 EZ40 .59 .64 EZ4I EZ80 .33 EZ8I .34 GY501 .82 GZ32 .59 GZ34 .70 EM87 EM84 EM87 EBC81 .41 EBF80 .46 EBF83 .50 EBF89 .38 EC92 .53 ECC33 1.76 ECC35 1.11 12BH7 .59 12BY7 .88 12K5 1.17 19AQ5 .59 30CI5 .82 30017 .94 6BQ7A .64 EM81 .23 .88 EBC4I 1.05 .53 EM80 EAF801 .88 EB91 .59 .36 EL84 EL506 .43 .88 EAF42 .59 1213E6 EL4I EABC80 2.34 12A6 1.17 12AC6 .82 I2AD6 .76 12AE6 .76 12AT6 .47 12AÚ6 .53 I2AV6 .59 12BA6 .53 .47 .82 .47 5Y3GT .53 5Z4G .53 1,76 KTW62 1.17 2.93 KT66 PABC80 PC86 PC88 PC97 PC900 PCC84 PCC85 PCC88 PCC89 PCC189 PCF80 PCF82 PCF84 PCF86 PCF200 .45 .70 .70 .52 .53 .41 1.17 1.46 5.83 ACI65 .33 AD140 .47 AD149 .64 ADl61 .59 AD162 .59 AF114 .33 AP115 .20 AFI21 .39 AF126 .23 BC107 .16 BC108 .16 BC109 .16 BC113 .33 BCI18 .29 BCZII .49 BF158.. .23 BF159 .33 BF163 .26 BFI80 .39 BY100 .23 BY126 .20 BY127 .23 0A91 .12 0A93 .12 0C23 .49 0C24 .49 OC25 .49 0C44 .13 0C45 .14 0C46 .20 0070 .16 0071 .14 0072 .14 0074 .29 0075 .14 0078 .20 0078D .20 .14 OC81 UY4I ÚY85 X41 X66 Z759 PY81 .41 PY82 .35 PY83 .45 PY88 .47 PY500 1.11 PY800 .47 .47 PY801 2.05 .70 .70 .77 .59 .76 019 U25 U26 U191 U801 UABC80 .47 UAF42 .70 UBC4I .70 .3S ÚRC81 .52 .70 .53 .56 .47 .47 .69 .56 1.17 1.17 PCF801 .59 PCF802 .59 PCF805 .82 PCF806 .59 PCH2001.00 .53 .59 1.17 PY33/2 .47 .41 PCF201 .41 PL81 PL82 PL83 PL84 PL504 PL508 PL509 UM80 .45 .53 .47 .64 .55 .94 .59 .70 .53 .43 .47 .47 .82 1.05 1.70 .53 QQV03/10 1.76 KTW63 2.63 1.46 .82 .39 .52 .52 .47 .40 .82 .47 1.76 .88 .82 .29 1.17 .35 .33 .35 .43 .59 .94 .35 PCL82 PCL83 PCL84 PCL805 PCL86 PEN45 PEN46 PL36 UBF80 UBF89 UC92 UCC84 UCC85 UCF80 UCH42 OCHS) UCL82 UCL83 UF4I 0042 .53 .47 .47 .53 .88 .53 .82 .88 .47 .45 OC8ID .I4 0082 .14 00821) .14 0083 .26 0084 .31 .64 .82 .88 .41 .52 .47 ÚF80 0585 UF89 UL41 UL84 0C202 0C205 .70 .49 .55 .55 All goods are unused and boxed, and subject to the standard 90 -day guarantee. Terms of business: Cash or cheque with order only. Despatch charges: -Orders below £10, add 25p extra per order Orders over £10 post free. Same day despatch. Terms of business available on request. Any parcel insured against damage in transit for only 5p extra per parcel. Please enclose S.A.E. with any enquiries. Many other types in stock. FOR SALE: Polarised relays, suitable for RTTY terminai units. £1.00. Box, No. G235. WANTED. Early radio books, prior to 1925. Box No. G236. ENGINEERS SERVICE SHEETS for Radios/TV's etc. 50p and s.a.e. Catalogue 20p and s.a.e. Hamilton Radio, 47 Bohemia Road, St. Leonards-on-Sea, Sussex. VALVES, RADIO, TV, TRANSMITTING. 1930 to 1975. 2,000 types stocked. Many obsolete. X78-TH41-2P-N78EBLI - EBL31 - ECC31 - EL37 - EN31 - TH4 - MKT4 PENDD4020 - PX4 - X81M , W61 - X101 - X109 - X145 X147 - Z21 - Z319 - 2359 - 6F33 - 61BT - etc. List 20p. We wish to purchase new and boxed valves. Cox Radio (Sussex) Ltd., The Parade, East Wittering, Sussex. Telephone: West Wittering 2023. BUILD THE MULLARD C.C. TV CAMERA. Complete kits now available from Crofton Electronics. Send large s.a e. for details to:- 124 Colne Road, Twickenham, Middlesex, TW2 6QS. Telephone: 01-898-1569. This 76page FREEboo BETTER JOB I -_ CUT OUT THIS COUPON - - - 1.I CHOOSE A BRAND NEW FUTURE HERE! Tick or state subject of interest. Post to_the address below. Manor lnd. Radio Sen., M.A.A./I.M.L FOR SALE: Four Bound Volumes of "Radio Constructor" August 1957 to July 1961. Offers? Not mint but good condition. Box No. G261. IELECTRICAL ICity&Guilds Wiring& Install. C & G Elec. Tech -Prim. Gen. Elec. Eng. C&GAuto Eng. Pract. ' ' fo I. Ekctronk TELECOMMS. C&G D Teleconua. Eng. D REFRIGERATOR SERVICING -MECHANICAL Eng. AUTO 0272-565472. self io-build build kiP)Q Radio Exam Manarage D Gen. Anno Prad. Radio & ENGINEERING Soc. of Eng. D Genen ) Meth. RADIO h ELECTRONICS Gen. Radio& TV Eng. E Welding Maine. Eng. R DRAUGHTSMANSHIP Inst. of En 8 D'men & Designers Gen. D'manship S G.C.E. -58'0' @ 'A' Lintel 'manshi Subjects -ever 10,000 Gump CONSTRUCTION h BUILDING gnat. of Build. D Clerk of Works Diploma tL]] Works Men. etc. etc. Ar Gen. Building Heat., Vent.& Aìr Con. Carpentry& Joinery Peieting&Dec.O C.E.L (Part l) Rep. Aulolog. S AERONAUTICAL 'ENGINEERING Air ng Board Gen. Diesel Eng. Maint.& Man. Dip. AutoDiesel Moist. D Motor Meth. D Service Station ENGINEERING ANTIQUE RADIO ENTHUSIASTS. For all your requirements in radio 1920 to 1945, contact Tudor Rees's Antique Wireless Service. Our full 1975 catalogue now available, price 40p post paid. Tudor Rees, 64 Broad Street, Staple Hill, Bristol, BS16 5NL. Telephone: C]ENGINEERING D a a PsuMl a Coedit', anyßor examinations. ,nations. ALDERMASTON COLLEGEeDept.TRE1 READINGRG74PFTRE 06- NAME (Block Capitals Please) . , ADORES! POSTCODF Age Omer subjects AA (Continued on page 700) -This helpful guide to success should be read by every ambitious engineer. .Send for this helpful 76 page FREE book now. No obligation and nobody will call on you. It could be the best thing you ever did. _ Inns. - 2527V, 55 off £160; 2533V, 10 off £75; MM5051, 20 off £65. Enquiries to Box No. G262. MORE PAY! WITH Do you want promotion, a better job, higher sties" shows you how to pay?"New Opportunities" get them through our low-oost home study course. There are no books to buy and you can pay-as -you -learn, , LONG DELIVERY or discontinued I.C.'s shows how! YOURSELF FOR A idi ed byC.A.C.C. HOME OF BRITISH INSTITUTE JUNE 1975 Member ofA;B.C.C OF ENGINEERING TECHNOLOGY 699 www.americanradiohistory.com NEW STYLE SELF -BINDER for "Radio & Electronics Constructor SMALL ADVERTISEMENTS (Continued from page 699) EXPERIMENTERS AND CONS'T'RUCTORS. Hundreds of items cheap. S.A.E. for List No. 10. Sample pack send 25p. Grimsby Electronics, Lambert Road, Grimsby, Humberside. FOR SALE: Regulated power supply. PU189, 0-15V, 0.4 amps, meter to monitor voltage. £14.40. Touch sensitive switch drive TTL or relay, £1.25. T. Edwards, Box No. G263. The "CORDEX" Patent Self -Binding Case will keep your issues in mint condition. Copies can be inserted or removed with the greatest of ease. Rich maroon finish, gold lettering on spine. Specially constructed Binding Cords are made from Super Linen of great strength, very hard twisted and twice doubled. They are attached to strong RUSTLESS Springs under tension, and the method adopted ensures PERMANENT RESILIENCE of the Cords. Any slack that may develop is immediately compensated for P Ani0 and the Cords will always cote rituétOR. remain taut and strong. It is impossible to overstretch the springs, as a safety check device is fitted to each. FIBRE OPTICS, OPTOELECTRONICS. Complete range fibre optics, photo -detectors, LED's, lenses, retroreflectors, polarisers, ultrasonic transducers. Send 9" x 6" s.a.e. for shortform price list: FIBRE OPTIC SUPPLIES, 2 Loudoun Road Mews, London NW8 ODN. WANTED: Everyday Electronics Volume 1 Nos. 1-5, May 1973. Also Practical Wireless January 1973. Price please to:- J. W. Farrar, 11 Constantine Road, North Bitchburn, Crook, Co. Durham. WANTED for cash or loan, circuit details of "Lerna-Kit" oscilloscope also Practical Wireless April 1971 and other issues containing "Workshop Oscilloscope". Box No. G264. JOIN THE INTERNATIONAL S.W. LEAGUE. Free services to members including Q.S.L. Bureau, Amateur and Broadcast Translation, Technical and Identification both Broadcast and Fixed Stations, DX CertifiDept. cates, contests and activities for the SWL and transmitting members. Monthly magazine, Monitor, containing articles of general interest to Broadcast and Amateur SWLs, Transmitter Section and League affairs, etc. League supplies such as badges, headed notepaper and envelopes, QSL cards, etc., are available at reasonable cost. Send for League particulars. Membership including monthly magazines, etc., £3.75 per annum. (U.K. and British Commonwealth), overseas $10.00 or £4.00. Secretary ISWL, 1 Grove Road, Lydney, Glos., GL15 5JE. - FOR SALE: Wireless World April 1964 - December 1974, Television August 1971 - December 1974. IOp each plus postage. S.A.E. for enquiries. Box No. G265. 4..-: HARDWARE SUPPLIES. Sheet aluminium, screws, nuts, washers, etc. Fascia panels in aluminium, individual requirements. Printed circuit boards, one-off or small runs, individual and for patterns published in this magazine Send 10p for list. Ramar Constructor Services, 29 Shelbourne Road. Stratford-upon-Avon. Warwicks. CV37 9JP. PRICE £11 o0 SHACK CLEARANCE. Diodes (from 1p), transistors (from 3p), valves, transformers, resistors, capacitors, computer boards, PSU, etc. S.A.E. list. Box No. G266. P. & P. 20p including V.A.T. Available only from:- Data Publications Ltd. 51 Maida Yale London W9 ISN WORLD DX CLUB covers all aspects of SWLing on Amateur and Broadcast Bands through its monthly bulletin "Contact". Membership costs £1.60 a year, Enquiries to Jo i Rush, 12 Northfield Road, Thatcham, Berks. WANTED: Decoder Type 6, ex Grundig radiogram KS560. Also wanted Tannoy truncated horn speaker. Leeves, Kingsnympton, North Devon. COLLECTORS: Dinky toys in fair condition, of approx. 1945 vintage. Offers? Box No. G267 (Continued on page 701) RADIO & ELECTRONICS CONSTRUCTOR 700 www.americanradiohistory.com PRECISION SMALL ADVERTISEMENTS POLYCARBONATE CAPACITORS (Continued from page 700) ALL HIGH STABILITY - EXTREMELY LOW LEAKAGE 440V AC 4-10%) 63V Range +4 % +-2% +-5% BC183/183L BC184/184L BC212/212L BC547 8C558A for 45p; 18 for 90p. for 59p; 24 for £1.00. BF194 12p BF196 13p BF197 13p 30p 20p AF178 BFY50 1N916 Bp; 6 IN4148 Sp; 6 20p 20p BFY51 BFY52 0071 12p 50p 2N3055 ; PLEASE ADD 25% V.A.T. TO ORDERS. PLEASE ADD 15p POST AND PACKING ON ALL ORDERS BELOW £5.00. Send S.A.E. for lists of additional ex -stock items. Wholesale price lists available to bona-fide companies. ALL EXPORT ORDERS ADD COST OF SEA/AIRMAIL. MARCO TRADING Dept. C6, The Old School, Edstaston, NR. WEM, Salop. Tel: WHIXALL (Salop) 4645 (STD 094872) (Props: MinicostTrading G269. ENGINEERS FOR SALE: Teak finish wooden amplifier sleeves. Internal 3i x 101 x 7 ins. £1.75 plus 50p P. & P. 29 Laburnham Grove, Winchmore Hill, London N21. Telephone: YOURSELF FOR A BETTER JOB WITH Do you want promotion, a better iob, higher pay? "New Opportunities" shows you how to get them through our low-cost home study course. There are n6 books to buy and you can pay -as -you -learn. MORE PAY! This helpful guide to success should be read by every ambitious Send for this helpful 76 page FREE book now. No obligation and nobody will call on you. It could be the best thing you ever did. . e IMCUT OUT THIS COUPON BON NMI Ma CHOOSE A BRAND NEW FUTURE HERE! - TREMENDOUS VALUE. Pack of over 500 components. Resistors, Capacitors, transistors, diodes, etc. Plus circuit boards crammed with components. Send only £1.50 to: Capital Components, BCM 3276, London WC15 6XX. I ' Tick or state subject of interest. Post to the address below. Build-As-You.Electronic Leant CITY &GUILDS Installations and Wiring & GUILDS Electrical Engineering PRACTICAL RADIO AND ELECTRONICS (with kit( Electrical Engineering Electrical Installations 1 ' and Wiring Electrical Computer Electronics Computer Programming TV Engineering Radio Servicing d Maintenance and Repairs ship hematics To Transistor Technology ALDERMASTON COLLEGE,OeptERRE NAME(Bly .k 13CITY fl General Radio Draughtsmen Electrical E Technicians CITY & GUILDS Exam etc. etc. Coaching for many major exam, 1ERE U6.8EADING RG74PF POSTCODE Age C E G.C.E. 58 '0' & 'A' LEVELS ADDRESS Other subjects. ' (] Telecommunications Radio Amateurs' CePtlel Pleee) Accredited b CA. C. (Continued on page 703) 11p 12p 14p 12p 12p 47K, 100K, 250K, 680K, 1M, 2.5M, & 5M. FOR SALE: 1,000 mixed resistors £1.00. 100 mixed 3-5-7W resistors £1.00, postage 25p. Switch cleaner 70p, 5 tins £2.50. Stereo cassette mechanism (just requires power supply and amplifier) £20.00. New 50cc 2 -stroke engine £17.50. 100 new records £10.00. Sample free. Box No. STEREO JACK PLUGS (standard) desoldered from new equipment, 50p for 5 (including P. & P.). Price for larger quantities on request. 5 Powderham Road, Exeter, Devon, EX2 9BS. 9p 12p 10p 12p 11p 2N3702/411p for 45p; 14 for 90p. for 27p; 12 for 48p. 1544 5p; 11 LOW PRICE ZENER DIODES: 400mW; Tol. +-5% at 5mA. Values available; 3V; 3.6V; 4.7V; 5.1V; 5.6V; 6.2V; 6.8V; 7.5V; 8.2V; 9.1V; 10V; 11V; 12V; 13V; 13.5V; 15V; 16V; 18V; 20V; 22V; 24V; 27V; 30V. All at 7p each; 6 for 39p; 14 for 84p. SPECIAL: 100 Zeners for £5.50. RESISTORS: High stability low noise carbon film 5%, 4 W at 40°C; 4W at 70°C. E12 series only - from 2.20 to 2.2M0 ALL AT 1p EACH; 8p for 10 of any one value; 70p for 100 of any one value. SPECIAL PACK: 10 of each value 2.20 to 2.2MO (730 resistors) £5.00. SILICON PLASTIC RECTIFIERS - 1.5 Amp - Brand new wire ended D027: 100 P.I.V. - 7p (4/26p); 400 P.I.V. - 8p (4/30p). BRIDGE RECTIFIERS: 24 Amp. 200V - 40p; 350V - 45p; 600V - 55p. SUBMINIATURE VERTICAL PRESETS - 0.1W only: ALL AT 5p each 500,1000, 2200, 4700, 6800 1 K, 2.2K, 4.7K, 6.8K, 10K, 15K, 22K, SUPERB INSTRUMENT CASES by Bazelli. Manufactured from heavy duty P.V.C. faced steel. Hundreds of radio, electronic and hi-fi enthusiasts are choosing the case they require from our range of over 200 models. Generous trade discount. Prompt dispatch. Free literature: Bazelli, Dept. No. 26, St. Wilfrids, Foundry Lane, Halton, Lancaster, LA2 6LT. CONSTRUCT Highest performance metal detector for approximately £1. Equal to £50 models. Simple illustrated plans. Send £1. C. H. Lucas, 241 Upminster Road South, Rainham, Essex. 0.47pF 1.0pF 2.2pF 4.7pF 6.8pF (1"xl;") BC107/8/9 BC114 BC147/8/9 BC153/7/8 BC182/182L 1 N914 6p; 8 RADIO & ELECTRONICS CONSTRUCTOR. Due to loss in warehouse fire, we require copies of the June and July 1973 issues. Cover price paid, remittance by return. Send to Data Publications Ltd., 57 Maida Vale, London W9 1 SN. WANTED: `Radio Constructor' General Purpose power supply unit, as featured in January 1971. Box No. G271. 50p 59p 62p (1â"x}") 71p (1$'x ") 75p 80p (2'41 91p (2"x4") (2"x1") £1.22 (1 (1"x") TRANSISTORS: FOR SALE: Touch sensitive switch, rain detector; drive TTL or relay, £1.25. Regulated power supply PU189 0-15V 0.4 amps, meter to monitor voltage, £14.40. Kilton Electronics. Box No. G268. 01-360 4499. VALVES, VALVES & MORE VALVES. 1930 to 1975, 2,000 types stocked. Many obsolete. List 20p. Transistors list 15p. Cox Radio (Sussex) Ltd., The Parade, East Wittering, Sussex. Telephone: West Wittering 2023. FOR SALE: Selenium solar cells 10p. 16 digit 2 memory calculator £75.00. 100 unmarked BZY88 50p. 50 unmarked 2W zeners 75p. 50 unmarked BC107/8/9 50p. Closed circuit camera construction manual £2.00. Low -band Pye Rangers, tested, £10.00. 8mm zoom cine camera £15.00. Box No. G270. x4") Shp 46p 36p 66p 56p 46p 80p 65p 55p £1.30 £1.05 85p £1.64 £1.29 £1.09 £2.00 £1.60 10.OpF £1.40 £2.75 £2.15 15.0pF £1.90 1.OpF £3.50 2.OpF 22.OpF £2.70 £2.55 TANTALUM BEAD CAPACITORS Values available: 0.1, 0.22, 0.47, 1.0, 2.2, 4.7, 6.8pF at 15V/25V or 35V; 10.0pF at 16V/20V or 25V; 22.OpF at 6V/10V or 16V; 33.OpF at 6V or 10V; 47.0pF at 3V or 6V; 100.0pF at 3V. ALL AT 10p EACH; 10 for 95p; 50 for £4.00. 0.1pF 0.22pF 0.25pF 0.47pF 0.5pF 0.68pF GUARANTEED BRAND NEW SEMICONDUCTORS. BC107 transistors gen. purpose n.p.n. 9p; BC177 transistors gen. purpose p.n.p. llp; 2N3055 transistors, high power 45p; IN4004 diodes, 400V p.i.v., lA 5p; IN4143 diodes 4p. Data sheets for each of the above 4p. P. & P. 15p per order. VAT extra. C.W.O. All orders despatched same day. Send large s.a.e. for full lists of semiconductors, caps., res., nuts, screws, etc. Nestra Electronics Ltd., Scott Street, Bognor Regis, Sussex. 06 ' Member of A.B.C.C HOME OF BRITISH INSTITUTE OF ENGINEERING TECHNOLOGY JUNE 1975 701 www.americanradiohistory.com REVOR OPTICAL & TECHNICAL 12/13 HENRIETTA ST., LONDON W.C.2 Tel. 01-836 4536 £6.00 4" POST FREE dia. lens FLEXIBLE MAGNIFIER RADIO MODELLER ELECTRON C I MODEL RADIO CONTROL Detailing both Theory and Practice, this book. by leading authority Paul Newell. has become the standard reference work. A brief historical survey leads up to a detailed description of proportional systems, with over 100 illustrations, including theoretical circuits and p.c. layouts for digital system. Price C2.25 an advanced 134 pages. V.K. Packing & Postage 32p theory and practice of WITH CAST IRON BASE, PRECISION GROUND AND POLISHED LENS, CHROME PLATED FRAME AND FLEXIBLE TUBE. IDEAL FOR HOBBIES, AND DETAILED WORK WHICH REQUIRES ON SALE NOW at all leading shops or direct from: - MODEL RADIO CONTROL RADIO MODELLER BOOKS DIVISION, BOTH HANDS FREE. Wellington Road, Middx. Hampton Hill, 64 S.A.E. FOR CATALOGUE (Subject to price ruling at the time of issue) development or systems proportmnal esplemed digital system des, mples and el feeteu all ercpn datele SMALL ADVERTISEMENTS Use this form for your small advertisement To: The Advertisement Manager, Data Publications Ltd., 57 Maida Vale, London W9 1 SN Please insert the following advertisement in the issue of RADIO & ELECTRONICS CONSTRUCTOR 15 words at 5p = 75p. ALL WORDING IN BLOCK LETTERS PLEASE I enclose remittance of being payment at 5p a word. Box Number, if required, 10p extra. MINIMUM 75p. NAME ADDRESS Copy to be received four weeks prior to publication. Published on the 1st of every month. RADIO & ELECTRONICS CONSTRUCTOR 702 www.americanradiohistory.com SMALL ADVERTISEMENTS (Continued from page 701) FREQUENCY LIST TRANSFERS. We have a limited supply of sheets of Dial Frequency Transfers in black. Short Wave frequencies 1.8Mc/s to 32Mc/s and 144Mc/s and 146Mc/s. Includes amateur band marker frequencies at 100kc/s points and other short wave frequencies from 2 to 32Mc/s at every 500kc/s points. Each frequency is repeated. Two sheets for 5p., five sheets for 10p., postage 4p. Data Publications Ltd., 57 Maida Vale, London W9 1 SN. WHEREVER YOU LIVE Partridge have the key, to the DX! World Record patented VFA aerial system guarantees a solution to your short wave reception problem. Stamp for brochure. Partridge Electronics Ltd., Broad stairs, Kent. PERSONAL JANE SCOTT FOR GENUINE FRIENDS. Introductions to opposite sex with sincerity and thoughtfulness. Details free. Stamp to: Jane Scott, 3/Con North St. Quadrant, Brighton, Sussex, BN1 3GJ. IF YOU HAVE ENJOYED A HOLIDAY on the Norfolk Broads, why not help to preserve these beautiful waterways. Join the Broads Society and play your part in determining Broadlands future. Further details from: The Hon. Membership Secretary, The Broads Society, "Icknield", Hilly Plantation, Thorpe St. Andrew, Norwich, NOR 85S. ARE YOU ADVENTUROUS? If so, you can make exciting new friends. Write: S.I.M. Computer Dating, (REC/3), 109 Queens Road, Reading, Berks. SPONSORS required for exciting scientific project. Norwich Astronomical Society are building a 30" telescope to be housed in a 20' dome novel being given by volunteers. Already supported by Industry and Commerce in Norfolk. Recreational. Educational. You can be involved. Write to: NAS Secretary. The Manse, Back Lane, Wymondham, Norfolk. YOUNG MAN DISABLED needs work at home. Electronic/ wire assembly. Would collect and deliver. Mr. B. Grimes, Llainwen, Glanrhyd, Cardigan, Wales, SA43 3PE. HOLIDAY ACCOMMODATION. Burwood Lodge Hotel, Dawlish Road, Teignmouth, South Devon. Especially suitable for parents with young children. Facing south, on the cliffs, direct access by private path to the sea. Mothers' kitchen, automatic washing machines, baby listening service. Licensed lounge. Ample free parking. ESSEX GARDENERS. Buy your Bedding and rock plants, shrubs, etc., also cacti from May's Nurseries, 608 Rayleigh Road, Hutton, Brentwood, Essex. Callers only. Monday to Saturday. - BARGAIN COMPONENT PARCELS contain some very useful bits and pieces. Save yourself Ls on these well selected parcels 2 kilos nett weight E1.80. BRAND NEW WIRE-WOUND RESISTORS 1-7 watts, selection, 100 for Eí.55. good POWER SUPPLIES FOR ELECTRONIC EQUIPMENT. J. R. Nowicki. Published recently in 2 vols. A full treatment of all power supplies is given. Includes rectification, inverters, transverters, silicon diodes and other electronic devices. With full circuit diagrams and component values. Originally published at £4.50 per volume. Bargain price £4 for the 2 volumes incl. postage. THE MOBILE RADIOTELEPHONE EQUIPMENT HANDBOOK. Gives circuits, data and illustrations plus some valuable modification details for COMMERCIAL RADIOTELEPHONE equipment. Price of this edition including postage £6.25. HOW TO MAKE WALKIE-TALKIES FOR LICENSED OPERATION. 40p, p.p. 15p. HOW TO MAKE 2M & 4M CONVERTORS FOR AMATEUR USE. Fully comprehensive. Contains circuits layouts, component lists, diagrams and full instructional notes. Price 60p. p.p. 15p. THE GOVERNMENT SURPLUS WIRELESS EQUIPMENt HANDBOOK. Gives circuits, data and illustrations plus valuable information for British/USA receivers, transmitters, trans/receivers. £4 including postage. DIRECTORY OF GOVERNMENT SURPLUS WIRELESS EQUIPMENT DEALERS! Gives details of surplus wireless equipment stores and dealers including addresses plus equipment and spares that they are likely to have available. A valuable book only 50p. p.p. 15p. GETTING THE BEST FROM YOUR COLOUR TV. R. Maude. Essential advice for colour TV engineers and owners. Could save you pounds. 50p. p.p. 1 5p. THE THEORY OF GUIDED ELECTROMAGNETIC WAVES. The most comprehensive book yet written about waveguides, transmission lines, cavity resonators. Over 500 pages. Ideal for anyone interested in Radar and UHF. Published at £11.50. Special offer £4.50 p.p. 50p. INTERNATIONAL DICTIONARY OF SEMICONDUCTORS. A 2 -volume electronics dictionary published at £16 available at less than half price. In 7 languages it proves an invaluable addition to any collection of electronics reference books. Contained are 1373 pages packed with information. In leather styled finish. Only £6.50, p.p. 50p. THE RADIO CONTROL MANUAL. Contains numerous plans, photographs and instructions. A large format hardback book published at £1.25. Bargain price 60p. p.p. 20p. THE THEORY AND DESIGN OF MAGNETIC AMPLIFIERS. 487 pages. Published at £1.75. Bargain price 75p. p.p. 25p. WORKED EXAMPLES IN ALTERNATING CURRENT. A must for the student, technician and electrical engineer. Contains numerous examples and how they were arrived at. Published at £1.25. Bargain price 60p. p.p. 20p. THE BARGAIN BOOK GAZETTE. Contains thousands of interesting new and out of print books at bargain prices. Subjects include all types of hobbies, collecting. 1001 interests. Published regularly and sent free on request. Dept. R. C. GERALD MYERS (Publisher & Bookseller), 138 Cardigan Rd., Headingly, Leeds 6, Yorks. (Callers Welcome). MORSE E SY BY THE RHYTHM METHOD ! FACT NOT FICTION. If you start RIGHT you will be reading amateur and commercial Morse within a month. (Normal progress to be expected.) Using scientifically prepared 3 -speed records you automatically learn to recognise the code RHYTHM without translating. You can't help it. It's as easy as learning a tune. 18-W.P.M. in 4 weeks guaranteed. For Complete Course 3 Records & Books send E4.95 including P.P.I. etc. (overseas surface mail E1 extra.) For further details of course Ring 01-6602896 or send large S.A.E. for explanatory booklet to:-S. BENNETT, G3HSC (Box 38) 45 GREEN LANE, PURLEY, SURREY SOCKET SETS £6.99p+p35p ASSORTED CAPACITORS, Silver Mica, Tubular and Disc Ceramics, Polystyrene. Tremendously good selection 300 for £1.55. SPECIAL OFFER-Metallised Polyester Capacitors by Brie, Mullard, etc. Values include 01/160V, 01/250V, 015/160V, .022/160V 033/160V, 047/160V, 068/160V, 1/160-250V, 22/160V, etc. This is a bargain not to be missed, 100 for E1.95. Please note all prices include Postage and V.A.T. MAIL ORDER ONLY XEROZA RADIO 1, EAST STREET, BISHOPS TAWTON, DEVON JUNE t l strong metal box with snap LJ Construction and repairs I made easy with this }" sq. drive high quality steel socket set. Bright chrome plated parts, catches. 39 piece (as illus.) with 11 AF,11 MM 811 BA sockets, Reversible ratchet, 2 extensions, sliding T -bar, flexible handle, tommy bar. 17 piece in plastic box with either 11AF, 11MM or 11 BA sockets, same accessories as 39 piece £4.49 p&p 35p. (State AF, MM or BA when ordering). SILHILL PRODUCTS Dept. REC6 226 Mary Street, Birmingham B12 9RJ. Tel. 021-440 3600, 703 1975 www.americanradiohistory.com PLAIN -BACKED NEW STYLE SELF -BINDERS Self -Binding Patent "CORDEX" will keep your copies in mint condition. Issues can be inserted or removed with the greatest of ease. Specially constructed Binding cords are made from Super Linen of great strength, very hard twisted and twice doubled. They are attached to strong RUSTLESS Springs under tension, and the method adopted ensures PERMANENT RESILIENCE of the Cords. Any slack that may develop is immediately compensated for, and the Cords will always remain taut and strong. It is impossible to overstretch the springs, as a safety check device is fitted to each. The Case PRICE 95p for your other magazines (max. format 74-." x 9+1 P. £t P. 20p COLOURS: MAROON OR GREEN including V.A.T. (If choice not stated, colour available will be sent) Available only from: ---- Data Publications Ltd. 57 Maida Vale London W9 1SN DATA BOOK SERIES DB5 TV FAULT FINDING DB6 RADIO AMATEUR OPERATOR'S HANDBOOK 132 pages. Price 90p, P. & P. 12p 88 pages. Price 70p, P. & P. lop DB16 RADIO CONTROL FOR MODELS DB17 UNDERSTANDING TELEVISION Now out of print 512 pages. Price £2.10, P. & P. 40p DB18 AUDIO AMPLIFIERS DB19 SIMPLE SHORT WAVE RECEIVERS 128 pages. 140 pages. I enclose Postal Order/Cheque for Price 53p, P. & P. 12p Price 80p, P. & P. 12p in payment for NAME ADDRESS (BLOCK LETTERS PLEASE) Ltd. Postal 'Orders should be crossed and made payable to Data Publications Overseas customers please pay by International Money Order. All publications are obtainable through your local bookseller. Data Publications Ltd., 57 Maida Vale, London W9 1SN PLEASE MENTION THIS MAGAZINE WHEN WRITING TO ADVERTISERS RADIO & ELECTRONICS CONSTRUCTOR 704 www.americanradiohistory.com www.americanradiohistory.com 60 67 80 100 90 15 IO 12 100 120 150 53 80 y 33 8 7 6 4 3 40 47 20 27 10 13 3.3 5.0 6.7 15052 5 20 15 IO 7.5 5 100S2 7.7 23 26 31 38 30 33 37 44 56 36 41 45 55 68 21 22 26 10 13 15 18 15 19 18 23 27 32 11 14 5.1 . 1.9 2.6 3.8 9.1 1.3 1.9 2.8 3.7 5.6 7.4 2.3 3.4 4.5 6.8 39052 27052 22052 26 32 17 19 21 11 13 15 6.4 8.5 6 7 8 8.5 9.8 22 13 15 18 12 15 18 15 9 10 12 11 5 4 3 1.5 2 1 10 12 991 0.5 0.75 1k52 6.1 7.3 3.7 4.9 2.5 1.8 _ 4.4 5.9 7.4 8.8 2.2 2.9 1.5 3.2 4.3 2.1 0.61 0.91 1.2 1.1 0.74 1.1 1.5 82052 680n 47052 The easiest way to determine the current in a resistor is to measure the voltage across it. The Table lists current, in m:%, for resistors from 10012 to 1 k12 at voltages up to 15 volts. Thus, a voltage of 3 volts across an 82012 resistor indicates a current of 3.7mA in that resistor RESISTOR CURRENT VALUES 30 40 50 60 70 1.5 2 1 0.5 0.75 Voltage o CONSTRUCTORS DATA SHEET o HENR5s Radio LARGEST SELECTION OF ELECTRONIC COMPONENTS AND EQUIPMENT. LOW PRICES- MEAN LESS VAT. VAT EXTRA You can build the Texan and Stereo FM Tuner TEST EQUIPMENT TEXAN 20 Karr/packing 35p L p U4311 Laboratory £52.00 meter U4312 20k0/V with Features glass fibre PC Board. Gardners low field transformer. 6 -IC's, 10 -transistors plus diodes, etc. Designed by Texas instruments engineers for Henrys and P.W. 1972 Supplied "°.q with full chassis work, detailed construction handbook and all necessary pans. Full input and oantrol facilities. Stabilised supply. Overall size 154 x 25 x 61' mains operated. Fee teak sleeve with (also built and tested D7.50) 1.10.75 £31.00 (carriage 50p) Features capacity diode tuning. lead and tuning meter ind,ators. stabilised powersupplyoperated High performance and sensitivity with unique station indication IC a ere( decoder' Overall size In teak sleeve e' x 23 x 6r. Complete kit with teak sleeve. £21.00 (Carriage 50p) =,; =-1 JOIN THE LARGE BAND OF HAPPY CONSTRUCTORS! NEW SPECIAL PURCHASE EMI SPEAKERS AM/FM TUNER MODULES SPECIAL These two modules together form a high quality AM/ FM tuner covering the long, medium and VHF broadest bands. Requires only 16 resistors and capacitors and a switch to complete. Supplied with circuits and spec. data. LP1179 FM Coverage 87-108MHz Bandwidth 300 kHz Selectivity 35 dB Signal to noise at limiting threshold 40 dB Audio ouput 7SreV U4315 20k0/V U4317 20k0/V PURCHASE in x 8 in chassis speakers (Carr./packing 30p each or 50p pr.) 150 TC 10 watts 8 ohms twin cone [220 450A Built-in tweeter 8 ohms [3.85 EW 15 watt 8 ohm with tweeter L6.25 35020 watt 8.15 ohm with tweeter 13 [8.95 each Polished wood cabinet L4.80 carr., etc. 35p each or 50p pair. LP1171 UHF TV TUNERS Built-in AGC Supply 6V negative earth LP 1179 and LP 1171 'AMPLIFIERS WITH CONTROLS volt 24+2f watts 8 ohms Mains 7+7 watts 8 ohms Mains 15+15 watts 8 ohms 9 volt 1}+1} watts 8 ohms 12 volt 3+3 watts 8 ohms E1210 12 SAC14 SAC30 CA038 CA068 8.25 11.75 14.95 6.95 10.50 MULLARD MODULES AM/Type LP 1157 LP 1185 line receiver UHF transistorised tuners UK operation. Brand new. (Post; packing 25p each). TYPE A variable tuning. Slow motion drive [3.00 TYPE B 4 -button push-button (ad/ustabie) [4.00 TYPE C variable tuning [250 TYPE D 6-button UHF/VHF L450 625 [4 each or 0750 pair. suitable Ferrite aerial 75p L2.50 £5.50 L5.85 E4.20 10.7 I.F. Unit LP 1186 10.7 F/M Tuner Gorier Perm. F/M Tuner U4324 20k0/V with case [9.85 U4313 20k0/V with steel case [13.80 U4317 200/V with case L17 00 U4341 33k0/V plus transistor steel case E11.00 U4323 20k0/V plus lkHz OSC with case 8.00 171-2 2016)/V slim type 5.95 THL33D (L33DX) 2k0/V Rdbust 7.50 TP5SN 20k0/V (Case L2) 10.75 TPIOS 2kG/V 8.50 TW2OS 20k0/V 13.00 TW5OK 50k0/V 1450 S100TR 100k0/V plus transistor tester 22.50 680E. Multi -tester 1TE40 AC Multivoltmeter PA -DISCOTHEQUE LIGHTING ellibIPMENT tu 2 6 volt FM tuner su 3) 12 volt version SD4912 Decoder for tu 3 SP621 6v stereo FM tuner 7.95 7.95 7.95 14.80 11.95 7.95 4.80 13.95 7.50 6.99 Sinclair FM tuner Sinclair decoder for above A1007 9v MW -AM tuner A1018 used FM tuner A1005M (S) decoder for above 5475 12v. Stereo decoder general purpose kit PREAMPLIFIERS Sinclair Stereo 60 Preamplifier E1300 Cart/fape/Mic Inputs 9 volt El 310 Stereo 3-30mV mag. cart. 9 volt FF3 Stereo 3enV tape head 9 volt 3402 Stereo 5-20mV Mag. cart. mains EQ25 Mono 3-250 mV Tape Cart Flay 9 volt 6.75 2.85 4.75 4.95 5.95 1.95 POWER SUPPLIES MAINS INPUT (chassis-rest cased) 470C 6/7}/9V 300 MA with ad'rs P500 9 volt 500 MA HC244R 3/6/74/9v. 400 MA stabilised l 24v, 28V. f 3.30 } ampp. P15 P108012 V 1A 4.70 P1081 45V 0.9A F12 41-12V 0.4-1 amp SE1OIA 3/6/9/12V, 1 amp stabilised P1076 3/41/6/74/9/12V f amp SE800A 1-15 VOLT 0-(A stabilised 2.25 3.20 5.50 3.30 3.30 4.70 7.80 7.15 12.75 4.20 17.50 SINCLAIR MODULES AND KITS ST80 stereo preamplifier Audio filter unit Z40 15 watt amplifier Z60 25 watt amplifier PZ5 power supplies for 1 or 2 Z40 PZ6 power supplies (STA3) for 1 or 2 Z40 PZ8 power supplies (STA3) for 1 or 2 Z60 Transformer for PZ8 [11.95 1.6.95 [5.45 [6.95 at CENTRE, TEL. 6963. 309 HENRY'S DISCO EDGWARE ROAD. EP27 Low Cost Seven Segment Led. Digit Height inch 61.35 pp 15p 500mHz L9.97 unit for above (arr 50p) [3.75 L450 Rechargeable Marriot Marriot Marriot Marriot Marriot Marriot BXIZE 343 } track erase } Track H/RPSingle Track Rec/Play Bogen Type UL290 Erase Miniature Stereo Cassette R/RPI Record/Play Rec/Play £225 p.p.15p I"BRAND 12v 1250R 1700R 1800R 2500R 4000R 12/5502 p.co Pco. 18/2402 p.c.o. 10.7 MHZ Miniature Ceramic IF 24v MODEL 35 STABILISED POWER SUPPLY Short-circuit proof power supply delivery up to 30v at 1A. Built-in colts and ammeters. t £34.00 A MODEL 40 WIDE RANGE AUDIO SIGNAL GENERATOR A high stability signal generator using the low distortion Wlen bridge principle. £34.00 MODEL 41 RF SIGNAL GENERATOR Covering 150kHz to 220MHz Output up to SOmV. RF in eight ranges. Built-in AF mod. £38.00 SIGNAL GENERATOR 43 RC BRIDGE Null indicating bridge for resistors and capacitors. Resistance range 1OR to 10M ±2% at Centre Scale. £23.50 MODEL 44 INDUCTANCE BRIDGE Measures 11H to 100H in four ranges 5% accuracy. Q measure- ment from 0.1-1.000 ±100/. MODEL 45 £34.00 DIRECT READING FREQUENCY £36.00 35 are internally powered from battery (extra). Carriage and packing all models 37p. ELECTRONIC FOOTBALL Ft TENNIS WITHFABULOU THES VIDEO SPORT ON YOUR OWN TV three' exciting electronic ball games S FOOTBALL TENNIS HOLE IN THE WALL on your own TV! Just plug Video Sport into the aerial socket of your TV and away you go. Completely safe for you, your children and your TV. Mains operated. OUR INCREDIBLE PRICE £34.72+VAT Play 4P 115 FILTER NOMBREX TEST EQUIPMENT 9v t NEW i tyre or mixed SN79 Seaes IC. 15' ,,; 100 -extra 20r, All models except Model I p.c.o. Paco. one -extra 25 METER 1850 p.co. 10',,; 10Hz to 100kHz in four ranges. Input from 10mV to 5v Special purchase 5 watt output 8-16 ohm load, 30 volt max. DC operation, complete with data. Price £1.50 each or 2 for [2.85. Printed Circuit Panels SOp. 2 2 12 -extra MODEL 75p 73p 45p 35p £150 Battery Miniature Relays 4 EXTRA DISCOUNTS semiconductors -Any [1.75 AMPLIFIERS 18/24v Pin XRSP/631Track High Erase Heads for XRSP 17/18/36 (XES11) STC & ITT 24v 14p 15p 17p 01.15 41.25 - Covering 150kHz to 300MHz in eight ranges. Highest range in harmonic. £24.50 for ew fluorescent tube. Supplied with instr. and tube 8330 p.p. 30p. p.co. p.co. Pin Pin Pin £2.50 £3.50 L5.00 EXCLUSIVE 5 WATT IC 2 2 8 Pin XRSP/171 Track High XRSP/184 Track Med. XRSP/364Track Med. Philips 12V Fluorescent Investor itOH 6/120 DIL SOCKETS MODEL 42 WIDE RANGE 2v 400mA/HR 50p p.p. 15p. CALCULATORS 40p per pair p.p. 150 DIGIT POCKET ELECTRONICS CALCULATORS 8 Demonstrations now in all HI FI Centres! SINCLAIR SL414 Plessey 5w Power Amp IC [7.98 40KHZ Ultra Sonic Transducers [4.00 2250 18.95 - fTE22D AF Generator 20Hz200kHz 19.95 HM350 in circuit transistor tester 19.50 T1-145 Compact transistor tester 14.75 G3/36 R/C ose 20Hz-200kHz £19.75 CD342 SWR Meter [5.75 SE350A De luxe signal tracer L12.95 SE400 Mini -lab all in one tester [15.50 C-15 Scope 500.000kHz (arr. L1) [43.00 Radio activity counter 0-10r f £4.98 47.98 19.50 f7E65 28 Range valve voltmeter fTE2OD RF Generator 120kHz- TAPE HEADS YOURSELF TTL. "7400 series" ICsfrom 16p each Cosmos "4000 series" ICs from 25p each Linear Op-Arms from 40p each Signotia Phase Lock ICs RCA Linear ICs TO3 Power Devices in PNP'and NPN 8C107 and "BC range" from 12p Range of "OC" types Plastic Power Devices, Rectifiers, Zener Diodes up to 10 watts Power Regulator ICs and many others. 18.50 19.75 (arr £1) modular and complete equipment. Lighting, mixing, microphones, accessories, speakers, amplifiers. lenses, etc., etc. FREE stock lists (Ref. No. 18) on request. CALL IN AND SEE FOR PRICES. TRANSISTORS AND INTEGRATED I.C.'s fTElS Grid dip meter 440kHz- Mains Without doubt U.K's best range of SEND NOW FOR OUR NEW FREE LIST No. 36 FOR OUR COMPLETE RANGE OF OVER 10,000 SEMI -CONDUCTOR DEVICES AT NEW LOW 14 16 24 28 NEW REVOLUTIONARY SUPER TESTER 6SOR FM AND AM TUNERS AND DECODERS P FREE: with 1.17.00 Case 28mHz AM Bandwidth 6.5kilz Sensitivity 1 mV FM5231 FM5231 with 1.10.00 HENELEC STEREO FM TUNER Mullard type LP 1179 and LP 1171 ON ALL ITEMS MULTIMETERS 20 WATT IC STEREO AMPLIFIER 4.90 p.p. 2Sp TAA 960 40KHZ AMP IC 21.4 p.p. 15p 0.71 p.p. 19p L11.00 Cambridge Built Cambridge Kit L9.00 Cambridge Memory Built Scientific Built Scientific Kit L17.50 £16.00 E13.50 NOW OPEN SUPERMARKET. COME AND BROWSE ROUND THE NEW COMPONENTS SUPERMARKET AT 404 EDGWARE ROAD. BARGAINS GALORE, GOODIE BAGS. COMPONENTS, ETC. Prices It descriptions correct at time of proof. Subject to change without notice VAT TO BE ADDED TO ALL ORDERS (EXPORT VAT FREE) E&OE ectronic entres 404-406 Electronic Components & Equipment 01 -402 8381 Hi Fi and Electronics 309 PA -Disco -Lighting High Power Sound 01-723 6963 Centres Open 303 Special offers and bargains store 9 ans -6pm All mail to 303 Edgware Road. London W2 18W Prices correct at time of preparation. Subject to change without notice. E.&O.E www.americanradiohistory.com HENRys Radio